UNIVERSITY  OF  CALIFORNIA 
SAN  FRANCISCO  LIBRARY 


A  I  LABORATORY    MANUAL 

U- 

OF 

EXPERIMENTAL      PHYSIOLOGY 

(Including  General  Physiology) 


BY 

LOIS  McPHEDRAN  ERASER,  M.A. 

Lecturer  in  Physiology,  University  of  Toronto 

F.  A.  HARTMAN,  PH.D. 

Professor  of  Physiology,  University  of  Buffalo 

J.  J.  R.  MACLEOD,  M.B. 

Professor  of  Physiology,  University  of  Toronto 

J.  M.  D/OLMSTED,  PH.D. 

Assistant  Professor  of  Physiology,  University  of  Toronto 


PM-M 


UNIVERSITY    OF    TORONTO    PRESS 

1922 


COPYRIGHT,  CANADA,  1919 

BY 
UNIVERSITY  OF  TORONTO  PRESS 


PREFACE. 

Experimental  physiology  is  now  recognized  as  a  fundamental 
subject  in  the  curriculum  of  the  medical  student  and  as  one  having 
a  most  important  place  in  the  training  of  the  student  of  biology. 
In  the  medical  course,  the  physiological  laboratory  serves  as  the 
portal  to  the  clinic;  as  the  testing  ground  where  the  student  may 
try  for  himself  in  how  far  the  known  laws  of  physics  and  chemistry 
can  be  successfully  employed  to  explain  the  normal  working  of  the 
human  machine.  No  more  can  theoretical  study,  or  demonstra- 
tion, by  itself  supply  a  correct  understanding  of  the  functions  spf 
the  living  body  than  could  similar  methods  in  training  an  engineer 
to  understand  an  engine.  Attempts  to  rectify,  by  operations  or 
by  drugs,  functional  derangement  in  the  diseased  animal  without 
a  practical  knowledge  of  the  normal  working  of  the  various  organs, 
both  isolated  and  as  a  whole  must  be  as  unjustifiable  as  attempting 
to  repair  a  complicated  piece  of  machinery  would  be  by  any  other 
than  a  practical  engineer. 

In  the  training  of  the  biologist,  experimental  physiology  finds 
its  value  because  it  teaches  how  to  interpret  the  relationship  be- 
tween structure  and  function.  For  the  advancement  of  physio- 
logical knowledge  it  is  essential  that  the  functions  of  the  lower 
animals  should  be  more  intensively  investigated  by  those  who 
have  been  trained  in  the  methods  of  the  experimental  physiologist. 
In  the  crowded  curriculum,  either  of  medicine  or  of  biology,  it 
is  impossible  to  find  an  amount  of  time  that  is  sufficient  for  the 
performance  of  more  than  a  few  of  the  fundamental  experiments 
in  each  of  the  main  subdivisions  of  the  subject  of  physiology. 
It  is  the  duty  of  the  teacher,  therefore,  to  select  these  experiments 
with  the  greatest  care  so  that  the  experience  which  the  student 
gains  in  their  performance  may  guide  him  aright  in  building  up 
his  knowledge  of  this  subject.  The  experience  gained  in  the  labora- 
tory is  to  serve  as  the  framework  upon  which  the  detailed  con- 
struction is  to  be  completed  by  fitting  on  to  it  in  their  proper  re- 
lationship to  one  another  the  other  facts  of  physiological  know- 
ledge, acquired  by  theoretical  study  and  demonstration. 

3 


4  EXPERIMENTAL  PHYSIOLOGY. 

While  admitting  these  principles  some  have  averred  that  the 
technical  difficulties  of  experimental  physiology  are  such  as  to 
make  it  impossible  for  the  average  medical  student  to  secure  a 
sufficient  number  of  results  to  justify  the  expenditure  of  time  and 
energy  required  in  the  laboratory.  This  is  a  fallacious  criticism 
for  it  assumes  that  every  experiment  to  be  of  value  should  be 
crowned  by  results  that  are  technically  flawless,  and  it  fails  to 
recognize  that  the  performance  of  the  work,  if  carefully  and  in- 
telligently done,  affords  that  personal  experience  without  which, 
in  a  highly  practical  science  like  medicine,  theoretical  knowledge 
by  itself  is  valueless  and  without  meaning. 

There  is,  however,  no  subject  of  the  medical  curriculum  in 
which  the  organization  and  arrangement  of  laboratory  courses  is 
more  difficult  for  classes  of  average  size  than  in  physiology.  In 
physics  and  chemistry,  as  well  as  the  various  morphological  sub- 
jects, the  material  for  the  laboratory  course  is  constantly  available, 
and  can  be  stored  away  for  future  use,  whereas  in  physiology  living 
material  must  be  provided  afresh  for  each  experiment  and  there 
must  be  constant  supervision  of  the  practical  work  to  see  that  the 
material  is  properly  used.  This  requires  that  the  student  be 
adequately  directed  as  to  how  he  should  proceed  with  the  experiment 
without  at  -the  same  time  stifling  originality  on  his  part  by  re- 
quiring him  explicitly  to  follow  detailed  directions  in  every  step. 
The  experiment  is  of  no  value  unless  it  is  performed  with  an  inquir- 
ing attitude  of  mind,  and  laboratory  directions  and  instruction 
should  be  no  fuller  than  is  necessary  to  guide  the  student  in  its 
general  performance. 

It  is  with  these  requirements  in  view  that  the  present  volume 
has  been  compiled,  and  while  the  authors  realize  full  well  its  many 
shortcomings  they  hope  that  the  practical  instruction,  not  only  in 
their  own  laboratories,  but  also  in  those  of  other  institutions  may 
be  assisted  by  its  publication. 

The  work  is  arranged  in  sections,  each  of  which  deals  with 
some  special  part  of  the  subject,  this  plan  being  adopted  because 
it  has  been  found  the  most  practicable  for  courses  designed  for 
large  elementary  classes,  as  well  as  for  smaller  groups  of  more 
advanced  students.  The  first  section  deals  with  the  fundamental 
experiments  in  the  physiology  of  isolated  muscle  and  nerve,  placed 


PREFACE.  5 

in  this  position  not  because  this  is  the  simplest  part  of  the  subject 
of  physiology  to  understand,  but  because  it  is  the  easiest  to  provide 
material  for  and  therefore  the  best  in  which  to  permit  of  sufficient 
practice,  so  that  the  student  may  become  familiar  with  the  methods 
of  physiological  technique.  The  two  following  sections  deal  with 
essential  experiments  illustrating  the  principles  of  the  heart  beat 
and  the  circulation  of  the  blood.  In  selecting  experiments  in  the 
last  mentioned  group  the  endeavour  has  been  made  to  apply  them, 
as  far  as  possible,  to  man.  A  certain  number  of  experiments  in 
which  other  mammalian  material  is  used  is,  however,  essential  in 
order  that  the  student  may  be  in  a  position  to  appreciate  the 
significance  of  results  which  will  later  be  demonstrated  to  him. 
These  demonstrations  are  described  in  the  last  sections  of  the 
manual  in  sufficient  detail,  so  that  the  various  steps  may  be  followed 
by  every  student  of  the  general  course  and  the  experiments  may 
be  performed  by  small  groups  of  more  advanced  students. 

In  the  experiments  on  the  central  nervous  system  the  decere- 
brate  or  spinal  animal  is  extensively  made  use  of,  as  recommended 
by  C.  S.  Sherrington  whose  work  in  this  direction  must  be  con- 
sidered as  the  most  important  contribution  that  has  recently  been 
made  to  the  advancement  of  the  teaching  of  practical  physiology. 
In  the  section  on  the  special  senses  a  relatively  larger  proportion  of 
theoretical  matter  is  given,  along  with  the  directions  for  the  experi- 
ments, partly  because  the  latter,  being  practically  all  subjective 
in  nature,  cannot  be  performed  unless  the  student  understands  fully 
what  he  is  looking  for,  and  partly  because  most  of  them  can,  and 
should  be  performed  in  the  study  rather  than  the  laboratory. 

A  great  difficulty  has  always  been  felt  by  instructors  in  physi- 
ology in  attempting  to  supply  simple  experiments  bearing  on 
the  chemistry  of  respiration  and  yet  there  is  no  part  of  physiology 
in  which  practical  experience  is  more  important,  if  the  student  is 
to  understand  the  principles  of  this  difficult  subject.  A  section  of 
the  manual  is  devoted  to  experiments  in  which  simplified  and  inex- 
pensive apparatus  for  gas  analysis  is  employed. 

Throughout  the  book,  besides  the  directions  for  the  experi- 
ments, a  brief  statement  is  given  of  the  theoretical  matter  which 
bears  on  them.  This  is  done  to  enable  the  student  to  appreciate 
the  object  of  the  experiment  and  to  guide  him  in  the  interpretation 


6  EXPERIMENTAL  PHYSIOLOGY. 

of  the  result;  but  the  latter  is  not  described  in  detail,  this  being  left 
for  the  student  to  determine  for  himself. 

While  the  general  plan  and  arrangement  of  the  book  is  the  work 
of  the  authors  jointly,  each  author  is  responsible  for  certain  chapters 
as  indicated  by  the  initials  given  in  the  table  of  contents. 

The  authors  wish  to  express  their  thanks  to  Miss  Marion  E. 
Armour  for  the  care  and  patience  which  she  bestowed  in  the  pre- 
paration of  the  drawings  for  the  illustrations,  many  of  which  are 
original  while  others  are  copied  from  other  texts,  acknowledgment 
for  which  is  given  in  the  legends. 

They  wish  also  to  thank  Miss  Jean  Halliday  for  her  assistance 
in  arranging  the  index  and  correcting  the  proof.  They  are  indebted 
to  Dr.  J.  P.  Eisenberger  for  a  final  reading  of  the  proof. 

In  the  present  edition  considerable  additions  have  been  made 
in  order  that  the  manual  may  cover  a  wider  field  of  experiments 
and,  so  it  is  hoped,  be  of  greater  assistance  in  other  institutions. 
A  section  on  General  Physiology  has  been  added  as  well  as  chapters 
on  Electrocardiography  and  Respiratory  experiments.  The 
methods  for  air  and  blood  gas  analysis  have  been  largely  rewritten 
since  it  is  now  possible  to  obtain  at  reasonable  cost  apparatus 
with  stopcocks,  thus  making  it  unnecessary  to  use  the  simpler 
apparatus  described  in  the  first  edition. 

We  wish  to  thank  Dr.  N.  B.  Taylor  for  valuable  assistance  in 
the  preparation  of  this  edition. 

LOIS    McPHEDRAN    ERASER. 

F.  A.  HARTMAN. 
J.  J.  R.  MACLEOD. 
J.  M.  D.  OLMSTED. 
The  University  of  Toronto. 


CONTENTS 


Chap. 

I. 

II. 
III. 
IV. 


Section  I. 

MUSCLE  AND  NERVE. 
F.  A.  H. 

PREFACE 

PRELIMINARY  TECHNIQUE 

VOLUNTARY  MUSCLE 

SMOOTH  MUSCLE  AND  CILIATED  CELLS 

PHYSIOLOGY  OF  NERVE.. 


Page. 

3 

9 

14 

42 

46 


V. 
VI. 


Section  IIA. 

CIRCULATION. 

F.  A.  H. 

CARDIAC  MUSCLE 61 

BLOOD  PRESSURE.     EFFECT  OF  CHEMICAL  SUBSTANCES  ON  THE 

BLOOD  VESSELS  AND  HEART 71 

Section  IIB. 

CIRCULATION. 

J.  J.  R.  M. 

VII.     HAEMODYNAMICS . 78 

VIII.     VASO  MOTOR  NERVES.    DEPRESSOR  NERVE.    CIRCULATION  TIME.      87 

IX.       POLYSPHYGMOGRAPH  TRACINGS 93 

Section  HI. 

REFLEX  ACTION. 

J.  J.  R.  M. 

X.     REFLEX  ACTION  IN  THE  FROG 98 

XI.     REFLEX  ACTION  IN  MAN.    REACTION  TIME  IN  MAN 104 

Section  IV. 
RESPIRATION. 

J.  J.  R.  M. 
XII.     ANALYSIS  OF  AIR  AND  COLLECTION  OF  ALVEOLAR  AIR 107 

XIII.  RESPIRATORY  EXCHANGE  IN  MAN 118 

XIV.  DETERMINATION  OF  THE  GASES  OF  BLOOD  BY  THE  PUMP  METHOD.     122 
XV.     DETERMINATION  OF  BLOOD  GASES  BY  THE  CHEMICAL  METHOD.     128 

XVI.     THE  DISSOCIATION  CURVE  FOR  OXYGEN  AND  THE  CO2  COMBINING 

POWER  OF  BLOOD 132 

Section  V. 

SPECIAL  SENSES. 

L.  McP.  F. 

XVII.     VISION 139 

XVIII.     ERRORS  IN  REFRACTION 149 

XIX.     EXAMINATION  OF  THE  REFRACTION  OF  THE  EYE  AND  OF  THE 

INTERIOR  OF  THE  EYEBALL 158 

XX.     RETINA 163 

XXI.     COLOUR  VISION 170 

XXII.     SIMULTANEOUS  CONTRAST.     VISUAL  JUDGMENTS.  .  178 

XXIII.  HEARING 182 

XXIV.  SKIN  SENSATIONS 192 

7 


CONTENTS. 


Section  VI. 
DEMONSTRATIONS. 
CIRCULATION  AND  RESPIRATION. 

J.  J.  R.  M. 

Chap.  Page. 
XXV.     THE  CIRCULATION  OF  THE  BLOOD  AND  LUMPH  AND  THE  RE- 
SPIRATION      199 

XXVI.     THE  DIRECT  DEMONSTRATION  OF  VASOCONSTRICTOR  BY  THE 

PLETHYSMOGRAPHIC  METHOD 202 

XXVII.     PERFUSION  OF  THE  EXCISED  MAMMALIAN  HEART.  . 206 

XXVIII.  MEASUREMENT  OF  THE  BLOOD  FLOW  THROUGH  THE  HANDS 
AND  FEET  BY  THE  CALORIMETRIC  METHOD.  ELECTROCAR- 
DIOGRAMS    210 

XXIX.     LYMPH  FORMATION 218 

XXX.     EXPERIMENTS  TO  DEMONSTRATE  THE  PUMPING  ACTION  OF  THE 

HEART  AND  THE  ACTION  OF  THE  VALVES 223 

Section  VII. 

DEMONSTRATIONS. 

DIGESTIVE  SYSTEM. 

J.J.  R.  M. 

XXXI.     THE  INNERVATION  OF  THE  SALIVARY  GLANDS: 226 

XXXII.  THE  CONTROL  OF  THE  PANCREATIC  SECRETION.  THE  SECRE- 
TION OF  BILE 228 

XXXIII.  EXPERIMENT  ON  THE  NORMAL  SECRETION  OF  SALIVA  AND 

GASTRIC  JUICE 231 

XXXIV.  THE  MOVEMENTS  OF  THE  OESOPHAGUS  AND  INTESTINE 236 

Section  VIII. 

DEMONSTRATIONS. 

THE  CENTRAL  NERVOUS  SYSTEM. 

J.J.  R.  M. 

XXXV.     REFLEX  ACTION  IN  THE  MAMMALIA 239 

XXXVI.  CEREBRAL  LOCALIZATION.  DECEREBRATE  RIGIDITY.  RECI- 
PROCAL INNERVATION.  FUNCTIONS  OF  SPINAL  ROOTS  IN 

THE  MAMMAL  (Doc) 243 

XXXVII.     THE  DECEREBRATE  CAT  1 247 

XXXVIII.    THE  DECEREBRATE  CAT  II.    THE  DECEREBRATE  PIGEON 251 

XXXIX.     THE  SPINAL  CAT 255 

Section  IX. 

GENERAL  PHYSIOLOGY. 

J.  M.  D.  O. 

XL.     PROPERTIES  OF  LIVING   PROTOPLASM.,     CHEMICAL   CONSTI- 
TUENTS    .' 258 

XLI.     PHYSICAL  CHEMISTRY  OF  CELLS 263 

X — II.     ENZYMES,  DIGESTION,  BUFFERS 267 

XLIII.     MOVEMENT.    ENVIRONMENT 269 

XLIV.     CIRCULATION  (CAPILLARY) 273 

APPENDIX 277 

INDEX..  281 


SECTION  I. 

CHAPTER    I. 

PRELIMINARY  TECHNIQUE. 

Electrical  Stimulation. — In  experimental  physiology  it  is 
necessary  in  many  instances  to  employ  an  artificial  stimulus  in 
order  to  cause  activity  in  the  tissue  to  be  studied.  Many  kinds  of 
stimuli  are  capable  of  doing  this,  but  to  most  of  them  there  are 
objections  when  used  on  nerve  or  muscle.  Mechanical,  chemical 
and  thermal  stimuli  are  all  more  or  less  injurious.  Moderate 
electrical  stimulation  on  the  other  hand  brings  these  tissues  into 
action  without  appreciable  injury.  As  this  is  the  means  by  which 
the  tissues  are  usually  stimulated,  we  will  discuss  briefly  the  prin- 
ciples involved  in  the  more  important  pieces  of  electrical  apparatus 
employed. 

For  a  source  of  current  either  a  dry  cell  or  a  dynamo  may 
be  used.  A  dry  cell  is  essentially  a  large  zinc  cup  serving  as 
container  in  which  is  suspended  a  carbon  cylinder.  A  small  amount 
of  water  containing  ammonium  chloride  held  by  gelatin  or  some 
inert  substance  fills  the  rest  of  the  container.  A  dry  cell  is 
essentially  a  wet  cell,  but  with  the  water  protected  from  spilling 
by  the  gelatin  "sponge'4'.  Whenever  the  carbon  and  zinc  are  con- 
nected by  a  conductor,  electrical  energy  is  set  free  by  the  solution 
and  is  transmitted  along  the  conductor.  It  has  been  found  that 
if  a  live  muscle  is  placed  in  the  electrical  circuit  that  the  tissue  will 
be  stimulated  at  the  time  the  circuit  is  made  and  again  when  it  is 
broken  provided  the  current  is  great  enough. 

Two  important  factors  must  be  kept  in  mind  in  the  use  of  an 
electric  current,  the  resistance  of  the  tissue  and  the  "pressure" 
of  the  current.  The  unit  of  "pressure"  is  the  volt.  Therefore  the 
amount  of  pressure  is  called  the  voltage.  By  increasing  the  voltage 
the  penetrating  power  is  increased  and  thus  the  physiological  effect 
augmented.  If  the  resistance  of  the  tissue  is  high  as  in  dry  skin,  a 

9 


10  EXPERIMENTAL  PHYSIOLOGY. 

greater  voltage  is  necessary  than  if  the  skin  has  been  moistened, 
because  moist  skin  is  a  better  conductor.  Dry  cells  are  made  to 
give  in  the  neighbourhood  of  one  or  two  volts.  Greater  voltage 
in  a  circuit  can  be  obtained  by  connecting  two  or  more  cells  in 
series,  i.e.,  zinc  to  carbon. 

In  most  of  your  work  the  current  generated  by  dynamos  in 
the  power  plant  will  be  used.  At  each  working  place  two  wires 
from  the  main  line  are  connected  with  a  metal  ribbon  of  high 
resistance.  Terminals  are  arranged  so  that  different  proportions 
of  this  ribbon  can  be  used  in  the  circuit,  thus  varying  the  amount 
of  voltage.  The  amount  of  voltage  obtained  can  be  estimated  by 
adding  the  total  voltages  between  the  two  terminals  employed. 
The  following  diagram  gives  the  voltages  between  terminals. 
T  represents  the  terminals  as  arranged  on  the  table. 
T8T8T4T4T4T2T2T 
abcdef  gh 

To  illustrate  the  method  of  finding  voltage,  connecting  a  to  f 
gives  28  volts;  f  to  h,  4  volts;  d  to  e,  4  volts. 

Besides  the  direct  current  one  can  use  the  induced  current  for 
stimulation.  It  is  well  known  that  if  one  wire  is  placed  near 
another  wire  which  carries  a  current,  a  brief  current  is  induced  in 
the  first  wire  at  the  time  of  breaking  the  circuit  in  the  second, 
likewise  a  current  is  induced  at  the  closing  or  making  of  the  circuit. 
The  wire  carrying  the  direct  current  is  called  the  primary  circuit, 
while  that  in  which  the  current  is  induced  is  called  the  secondary 
circuit.  Greater  effects  can  be  produced  by  having  a  coil  of  well 
insulated  wire  surrounding  a  soft  iron  core  as  the  primary  circuit 
element  and  another  coil  of  insulated  wire  as  the  secondary  element. 
These  two  coils  are  arranged  on  a  stand  for  convenience,  the  whole 
apparatus  being  termed  an  inductorium  (Fig.  1).  The  chief 
advantages  of  the  induced  over  the  direct  current  for  purposes  of 
stimulation  are;  first,  the  voltage  is  very  much  greater  so  that 
high  resistances  can  be  overcome  and,  secondly,  it  can  readily  be 
altered  in  strength. 

Note  that  the  inductorium  is  so  arranged  that  by  connecting 
binding  post  1  and  2  a  single  momentary  current  is  induced  in  the 
secondary  coil  when  the  circuit  is  either  made  or  broken  in  the 
primary  coil;  and  that  by  connecting  binding  posts  1  and  3  brief 


PRELIMINARY  TECHNIQUE.  11 

currents  are  continuously  induced  in  the  secondary  coil  due  to  the 
constant  interruption  of  the  current  in  the  primary  by  the  vibrating 
spring.  The  latter  effect  is  called  a  tetanizing  current. 

It  has  been  found  that  the  least  induced  current  is  produced 
when  the  secondary  is  at  right  angles  to  the  primary;  from  this 
position  the  current  is  increased  more  and  more  as  the  secondary 
becomes  more  nearly  parallel.  In  addition  to  the  angular  relation- 
ship, the  distance  between  the  two  coils  determines  the  strength 
of  current  induced,  the  closer  they  are  the  greater  the  effect. 


FIG.  1.  Inductorium:  (a)  Primary  Coil;  (b)  Secondary  Coil;  (c)  Bar 
for  short-circuiting  the  secondary  terminals.  Connect  the  source  of 
supply  to  1  and  2  for  single  shocks  and  to  1  and  3  for  a  succession  of  rapid 
shocks. 

Experiment  1. — Try  the  following. — -1.  Connect  the  electrodes  to 
two  terminals  on  the  table  so  as  to  obtain  2  volts.  Touch  the 
tongue  with  the  electrodes  and  then  make  and  break  the  circuit 
by  means  of  the  switch.  Repeat  with  increasing  voltage. 
Describe  the  effects  at  make,  at  break  and  during  the  passage 
of  the  current. 

2.  Connect  the  binding  posts  1  and  2  (Fig.  1)  of  the  primary 
coil  to  4  volts  on  the  table,  with  a  simple  key  in  the  circuit. 
Connect  the  electrodes  to  the  end  of  the  rods  upon  which  the 
secondary  slides.  With  the  secondary  coil  far  out  and  parallel 


12  EXPERIMENTAL  PHYSIOLOGY. 

to  the  primary  coil  stimulate  the  tongue  by  making  and  break- 
ing the  primary  circuit.  Move  the  secondary  closer  and  closer 
to  the  primary  coil  and  note  the  effect  produced  on  the  tongue. 
Again  move  the  secondary  out  into  such  a  position  that  it  just 
clears  the  primary  coil.  Now  study  the  effect  of  tilting  the 
secondary  coil. 

The  Graphic  Record. — By  the  use  of  a  lever  it  is  possible  to 
magnify  muscle  contraction.  The  movement  of  this  lever  is  re- 
corded on  smoked  paper.  The  kymograph  is  devised  for  carrying 
the  smoked  paper. 

Glazed  paper  is  wrapped  tightly  around  the  drum  of  the  kymo- 
graph so  that  the  glaze  is  outward.  The  gummed  end  is  fastened 
to  the  opposite  end  so  that  the  paper  will  not  slip  and  the  writing 
point  of  the  lever  will  not  catch  on  the  overlap.  The  drum  is 
held  in  the  smokiest  part  of  a  gas  flame  while  being  rotated  rapidly 
on  the  brass  tube  which  is  maintained  horizontally  by  hand.  In 
this  way  a  uniform  coating  of  carbon  can  be  obtained  on  the 
paper.  A  light  chocolate  colour  is  to  be  preferred  to  a  deep  black 
because  there  is  less  danger  of  burning  the  paper. 

A  small  triangular  piece  of  photographic  film  or  waxed  paper  is 
fastened  by  a  bit  of  wax  to  the  end  of  the  lever  in  order  to  serve 
as  a  writing  point.  The  lever  is  always  on  the  right  hand  side  of 
the  drum  so  that  when  the  latter  is  rotated  it  pulls  away  from  the 
writing  point.  The  lever  must  be  at  a  tangent  to  the  curved  surface 
of  the  cylinder  in  order  to  prevent  the  writing  point  leaving  the 
smoked  surface  when  it  rises.  The  writing  point  may  be  bent 
inward  to  keep  the  rest  of  the  lever  free  of  the  drum. 

When  ready  to  remove  the  paper  from  the  drum,  it  is  cut  at 
the  overlap  by  a  sharp  knife  in  such  a  way  that  the  knife  strikes 
the  under  paper  and  not  the  drum.  A  corner  of  the  paper  is 
grasped  against  the  edge  of  the  drum  with  the  other  hand  so  that 
it  will  not  fall.  At  this  stage  the  record  may  be  placed  on  the  table 
and  lettering  or  other  explanatory  matter  inscribed.  It  is  well 
to  place  your  name  and  date  on  each  record.  The  record,  with 
smoked  side  up,  is  passed  once  through  a  rosin-alcohol  solution 
(120  gm.  rosin  to  1,000  c.c.  of  95%  ethyl  alcohol)  and  then  hung 
over  the  tray  to  drain.  When  dry  the  parts  desired  are  to  be  care- 
fully cut  out  and  preserved  in  the  note  book. 


PRELIMINARY  TECHNIQUE  13 

Instruments  for  Dissection. — Each  student  should  supply 
himself  with  the  following:  Two  pairs  of  scissors,  one  heavy  the 
other  fine;  two  pairs  forceps,  one  heavy  the  other  fine;  one  dental 
probe,  one  strabismus  hook,  one  scalpel,  one  small  serre  fine  and 
one  haemcstat.  The  fine  scissors  and  fine  forceps  are  to  be  used 
only  in  delicate  dissection.  In  order  to  do  the  best  work  the  cutting 
instruments  must  be  kept  sharp. 


CHAPTER    II. 
VOLUNTARY  MUSCLE. 

One  of  the  most  striking  characteristics  of  living  things  is 
their  power  of  movement.  This  is  not  so  marked  in  plants,  but 
all  animals,  even  those  which  lack  the  ability  to  move  from  place 
to  place,  possess  organs  which  are  constantly  in  motion.  The  power 
of  contractility  which  is  inherent  in  all  protoplasm  is  developed 
to  its  highest  degree  in  muscular  tissue.  Thus  practically  every 
life  process  which  involves  the  movement  of  masses  of  tissues  is 
brought  about  by  the  action  of  muscles,  e.g.,  breathing,  circulation 
of  the  blood,  passage  of  the  food  down  the  alimentary  tract,  etc. 

A  portion  of  the  muscle  of  the  body  is  under  the  control  of 
the  will.  Upon  this  muscle  we  depend  for  locomotion,  movement 
of  our  hands,  eyes  and  the  like.  Such  muscle  is  distinguished  by 
the  fact  that  it  is  composed  of  fibres  with  a  characteristic  cross 
striation. 

STIMULATION. 

Various  kinds  of  stimuli  will  cause  muscle  to  contract,  but  before 
deciding  upon  the  best  form  to  use  we  must  know  where  to  apply 
the  stimulus.  Normally  the  muscle  fibres  are  called  into  action 
by  impulses  passing  along  the  nerve  fibres.  Artificial  stimuli  can 
be  effectively  applied  along  the  same  path.  Thus  mechanical, 
thermal,  chemical  and  electrical  changes  can  cause  a  muscle  to 
act  through  its  nerve.  Any  of  these  changes  to  be  effective  must 
not  only  be  of  sufficient  magnitude  but  must  be  abrupt.  A  nerve 
slowly  compressed  may  be  without  effect,  but  if  quickly  pinched, 
a  twitch  of  the  muscle  results. 

Of  all  artificial  stimuli,  an  electric  current  is  not  only  the  most 
effective,  but  also  the  least  injurious  to  nerve.  Mechanical  and 
thermal  changes  great  enough  to  have  an  effect  injure  the  tissue 
permanently  so  that  these  stimuli  can  be  used  only  a  single  time. 
Chemical  stimulation  if  not  harmful,  is  at  least  difficult  to  control. 
Moderate  electrical  changes  have  none  of  these  objections. 

14 


VOLUNTARY  MUSCLE.  15 

Although  we  are  most  interested  in  the  physiology  of  mam- 
malian muscle,  we  employ  muscles  from  cold-blooded  animals 
because,  while  similar  in  function,  they  survive  for  a  much  longer 
period  when  deprived  of  their  circulation. 

Experiment  2.— Nerve -Muscle  Preparation. — Kill  a  frog  in  the 
following  manner:  By  bending  the  frog's  head  down,  a  depression 
between  the  skull  and  first  vertebra  can  be  felt  on  sliding  a 
blunt-pointed  seeker  back  along  the  mid-line  of  the  top  of  the 
skull.  Make  a  short  traverse  cut  in  the  skin  at  this  point. 
Plunge  a  seeker  or  pithing  wire  into  this  depression  and  turning 
the  instrument  forward  into  the  skull  cavity  destroy  the  brain. 
Next  destroy  the  cord  by  passing  the  seeker  down  into  the 
spinal  cord.  If  the  frog  is  properly  pithed  it  immediately 
becomes  limp.  Later  the  muscles  may  become  less  flaccid.  A 
frog  thus  prepared  is  dead  although  the  heart  and  other  tissues 
may  live  for  a  few  hours.  There  can  be  no  pain  whatsoever. 
This  method  of  killing  a  frog  is  called  "pithing". 

Slit  the  skin  around  a  pithed  frog  just  behind  its  fore  legs 
and  remove  the  skin  from  the  posterior  half  of  the  animal. 
Lay  the  preparation  ventral  down  on  a  clean  glass  plate  and 
keep  it  moistened  with  0.7%  salt  solution.  Carefully  dissect 
out  the  sciatic  nerve  on  one  side  by  separating  the  muscles  on 
the  dorsal  aspect  of  the  thigh  and  freeing  'the  nerve  from  the 
surrounding  tissues.  Always  lift  the  nerve  with  a  glass  hook 
and  avoid  stretching  it.  Trace  the  nerve  to  its  exit  from  the 
spinal  column.  Split  the  spinal  column  in  two  at  this  point. 
Leave  parts  of  two  or  three  vertebrae  attached  to  the  nerve 
to  serve  as  a  convenient  way  of  handling  the  nerve  and  cut 
the  remaining  tissue  away. 

By  means  of  the  vertebrae  raise  the  roots  of  the  sciatic  nerve 
and  clip  beneath  it  until  it  is  free  down  to  the  knee.  Cut  the 
Tendo  Achilles  and  separate  the  gastrocnemius  from  the  other 
muscles  as  far  as  the  knee.  Cut  the  other  muscles  and  the 
tibia-fibula  just  below  the  knee.  Cut  away  all  the  muscles 
above  the  knee  and  the  femur,  leaving  about  half  an  inch  of  bone. 
In  making  a  nerve-muscle  preparation  one  must  always 
remember  that  slight  injury  to  muscle  or  nerve  may  ruin  it 
for  experimental  purposes.  Such  injury  may  be  caused  by 


16  EXPERIMENTAL  PHYSIOLOGY. 

stretching,  pressing,  drying,  or  chemical  agents.  The  loss  of 
water  may  be  prevented  by  keeping  the  muscle  in  air  saturated 
with  water  vapour  or  by  frequently  applying  water  to  the 
exposed  surface.  But  bathing  the  muscle  with  water  produces 
consequences  as  serious,  perhaps,  as  drying,  because  salts  and 
other  substances  are  drawn  out  of  the  cells  by  osmosis.  Now 
if  we  add  the  same  salts  in  the  same  percentage  as  occurs  in 
the  tissue  to  the  water  which  is  used  to  bathe  the  muscle 
such  a  solution  can  be  used  to  prevent  evaporation  without 
taking  salts  from  the  cells.  NaCl  dissolved  in  water  to  the 
extent  of  0.7%  produces  an  isotonic  solution  somewhat  similar 
to  the  tissue  fluid  of  the  frog,  and  is  therefore  useful  for  keeping 
the  tissues  moist  without  the  injurious  effect  of  pure  water. 
Apply  this  solution  to  both  the  nerve  and  muscle  frequently. 

NERVE-MUSCLE  PREPARATION. 

Experiment  3. — Different  Kinds  of  Stimuli. — Fix  the  femur 
of  a  nerve-muscle  preparation  in  the  flat-jawed  clamp  fastened 
to  a  stand.  Clamp  the  nerve  holder  to  the  stand  just  below 
and  then  lay  the  whole  sciatic  nerve  on  the  glass  plate.  Fasten 
the  muscle  lever  underneath.  Attach  the  tendon,  by  means 
of  a  hooked  pin  to  the  lever.  Now  adjust  the  after-loading 
screw  so  that  the  muscle  supports  no  weight  but  is  fully  ex- 
tended when  at  rest.  Place  a  ten  gram  weight  upon  the  scale 
pan  (Fig.  2).  In  practically  every  experiment  in  muscle-nerve 
physiology,  the  muscle  is  after-loaded  in  this  fashion.  This 
after  loading  keeps  the  muscle  extended  and  takes  the  slack 
so  that  when  contraction  occurs  there  will  be  no  sudden  jerk 
which  might  injure  the  muscle  fibres.  Arrange  the  lever  so 
that  it  will  write  on  the  smoked  paper  of  the  kymograph  and 
obtain  records  with  the  following  types  of  stimuli : 
MECHANICAL. — Pinch  the  nerve  near  its  end  with  forceps.  Can 
you  get  a  response  the  second  time  from  the  same  place? 
CHEMICAL. — Place  a  few  salt  crystals  on  the  fresh  end  of  the 
nerve,  the  injured  portion  having  been  cut  away.  After  a  few 
contractions  of  the  muscle  thoroughly  remove  the  salt  with 
isotonic  salt  solution. 


VOLUNTARY  MUSCLE. 


17 


THERMAL. — Touch  the  fresh  end  of  the  nerve  with  a  hot  glass 

rod. 

ELECTRICAL. — Connect  the  stimulating  electrodes  directly  to 

the  current  supply  on  the  table  but  with  a  simple  key  in  the 

circuit.     Try  the  effect  of  make  and  break,  beginning  with  2 

volts  and  then  increasing  the  current. 


FIG.  2.  Apparatus  for  recording  muscle  contraction:  (a)  femur  clamp;  (6)  nerve  holder 
(c)  electrodes;  (d)  muscle  lever;  (e)  signal  magnet;  (/)  after-loading  screw;  (g)  wires  connected  in 
the  primary  circuit. 

Next  connect  the  electrodes  to  the  secondary  coil  of  the 
inductorium  using  a  primary  current  of  2  volts;  stimulate  with 
make  and  break  shocks  of  different  intensities. 

Compare  the  effects  of  make  and  break  in  direct  and  indirect 
currents. 

Minimal  and  Maximal  Stimulation. — Beginning  with  a 
stimulus  too  weak  to  cause  contraction,  then  very  gradually 
increasing  its  strength,  a  point  is  reached  where  a  slight  contraction 


18 


EXPERIMENTAL  PHYSIOLOGY. 


results.  This  is  called  the  minimal  stimulus.  In  other  words  it  is 
the  least  stimulus  which  will  cause  a  contraction.  On  the  other 
hand  the  maximal  stimulus  is  the  least  stimulus  which  will  produce 
maximal  contraction.  When  a  series  of  stimuli  of  increasing  strength, 
beginning  with  the  minimal,  is  sent  into  a  nerve  or  muscle,  one 
obtains  a  graded  response  (Fig.  3).  This  is  true  no  matter  how 
finely  graded  is  the  increase  of  the  stimulus.  (See  all-or-none 
principle,  p.  61). 

Experiment  4. — Response  to  Stimuli  of  Different  Intensities. 
—For  this  experiment  employ  a  muscle  which  has  been  cut 
away  from  its  nerve.  Instead  of  using  ordinary  stimulating 
electrodes  connect  one  terminal  of  the  secondary  coil  to  the 


i 


FIG.  3.     Contractions  produced  by  graded  stimulation.     Secondary  coil  moved  5  mm. 
at  each  step.     Both  make  and  break  shocks  employed.     Make  contraction  begins  at  m. 


femur  end  of  the  muscle  by  wire  and  in  a  similar  way  connect 
the  other  terminal  to  ihe  binding  post  on  the  muscle  lever. 
Then  a  bit  of  fine  wire  is  wound  around  the  tendon  and  finally 
fastened  to  the  coarser  wire  at  the  binding  post  on  the  muscle 
lever.  In  this  manner  a  current  can  be  passed  through  the 
muscle. 

Starting  with  the  secondary  as  far  as  possible  from  the 
primary,  cautiously  move  it  forward  by  stages,  each  time 
stimulating  the  muscle  with  a  make  and  break  shock.  When 
the  first  perceptible  contraction  is  produced  you  have  reached 
the  threshold.  Between  each  stimulation  move  the  drum  a 


VOLUNTARY  MUSCLE.  19 

short  distance  by  hand,  not  more  than  1  mm.  Now  carefully 
move  the  coil  toward  the  primary  so  that  at  each  position 
there  is  produced  a  slightly  greater  contraction  than  before. 
Distinguish  the  "make"  and  "break"  contractions  on  the 
record  by  the  letters  nt  and  b  placed  beneath.  Also  designate 
the  position  of  the  secondary  coil.  It  is  possible  by  carefully 
increasing  the  stimulus  to  obtain  a  graduated  series  of  con- 
tractions from  both  the  make  and  break  shocks  (Fig.  3).  When 
the  series  is  complete,  indicate  the  minimal  and  maximal 
stimuli. 

Discuss  the  application  of  the  all-or-none  principle  to  your 
records. 

INDEPENDENT  EXCITABILITY  OF  MUSCLE. 

Ordinarily  the  question,  as  to  whether  a  muscle  could  respond 
if  its  nerves  were  absent,  is  of  academic  interest.  But  if  we  wish 
to  test  the  power  of  a  muscle  which  has  lost  its  voluntary  function 
by  injury  to  the  nerve,  we  find  long  after  the  nerve  has  degenerated, 
that  the  muscle  responds  to  direct  electrical  stimulation.  It  can 
also  be  shown  that  with  the  nerve  intact  but  with  the  connection 
between  the  nerve  and  muscle  paralysed,  the  muscle  is  still  excit- 
able. This  can  be  done  by  the  injection  of  the  poison  "curare" 
into  the  circulation.  After  a  few  minutes  has  elapsed,  stimulation 
of  the  nerve  no  longer  affects  the  muscle,  while  stimulation  of  the 
muscle  causes  it  to  contract.  From  such  experiments  as  these 
it  appears  that  muscle  can  contract  without  the  mediation  of 
either  nerve  fibres  or  motor  end  plates. 

Experiment  5. — The  sciatic  nerves  are  exposed  in  each  leg  of  a 
frog  which  has  the  brain  destroyed.  A  ligature  is  passed  under 
one  sciatic  and  around  the  thigh  and  tied  tightly  so  as  to 
occlude  circulation  in  that  leg.  A  few  drops  of  1%  curare 
solution  are  injected  into  the  back  of  the  frog.  From  time  to 
time  stimulate  each  sciatic  nerve  with  induction  shocks.  In  a 
few  minutes,  the  leg  with  intact  circulation  refuses  to  respond 
or  else  responds  very  much  less  than  the  ligated  leg.  When 
this  stage  has  been  reached  stimulate  the  muscles  of  the  un- 
ligated  leg  directly.  Their  response  demonstrates  that  the 


20  EXPERIMENTAL  PHYSIOLOGY. 

muscle  is  independently  irritable  for  the  nervous  impulse  has 
been  ruled  out.  This  has  been  accomplished  by  paralysis  of 
the  tissue  connecting  nerve  fibres  with  muscle  fibres,  for  it 
can  be  shown  that  impulses  still  travel  along  the  nerve.  How 
does  this  experiment  show  the  locus  of  action  of  the  drug  curare? 

EXTENSIBILITY    AND    ELASTICITY    OF    MUSCLE. 

In  the  body  more  or  less  tension  affects  each  muscle.  The 
weight  of  various  parts  and  the  antagonistic  action  of  opposing 
muscles  contribute  to  this  tension.  The  result  is  a  certain  amount 
of  elongation.  This  can  be  shown  by  fastening  a  weight  to  an 
isolated  muscle.  When  the  weight  is  removed  the  muscle  soon 
regains  its  former  length,  that  is,  it  exhibits  elasticity. 

The  amount  of  elongation  increases  with  increase  in  tension, 
but  with  each  additional  tension  the  elongation  is  proportionately 
less.  To  illustrate — suppose  X  grams  cause  an  elongation  of  2  mm. 
Then  2  X  grams  will  not  cause  4  mm.  elongation  but  something 
less,  perhaps  3  mm.  3  X  grams  would  produce  4.5  mm.  elonga- 
tion, etc. 

Beyond  a  certain  tension  the  reverse  is  true;  the  elongations 
per  unit  increase  being  greater  and  greater  with  each  step.  Where 
this  reversal  begins  the  so-called  elastic  limit  has  been  passed. 
Finally  there  comes  a  time  when  the  muscle  fibers  are  ruptured. 

Needless  to  say  a  muscle  should  not  be  extended  beyond  its 
elastic  limit. 

In  conclusion,  tension  is  very  useful  in  keeping  a  muscle  pre- 
pared for  contraction,  for  we  find  that  a  muscle  will  not  only 
respond  more  quickly  but  more  energetically  if  it  is  under  a  certain 
amount  of  tension.  This  condition  holds  in  the  body. 

Muscle  can  be  stretched  and  again  regain  its  resting  length 
when  the  force  producing  the  change  is  removed.  It  differs  some- 
what from  a  rubber  band  in  that  it  does  not  respond  by  equal 
extension  for  equal  increments  of  weight  as  the  total  weight  in- 
creases nor  does  immediate  recovery  occur  when  the  weights  are 
removed. 
Experiment  6. — Isolate  either  of  the  two  large  muscles  (gracilis 

and  semi-membranosus,  Fig.  4)  on  the  inside  of  the  thigh  of  a 


VOLUNTARY  MUSCLE.  21 

frog;  cut  through  the  tibia  below  its  insertion  and  through  the 
femur  above  the  knee.    Remove  it  with  the  bone  from  which  it 


FIG.  4.  A  ventral  view  of  frog.  1,  M.  Gastrocnemius. 
2,  M.  Tibialis  anticus.  3,  M.  Gracilis.  4,  M.  Adductor  mag- 
nus.  5.  M.  Sartorius.  6.  M.  Adductor  longus.  7,  M.  Vastus 
internus.  8.  N.  Vagus.  9,  N.  Glosso-pharyngeal.  10,  N.  Hypo- 
glossal.  11,  N.  Superior  laryngeal. 

B.  Dorsal  aspect  of  hind  leg.  12,  M.  Rectus  anterior. 
IS.M.Vastusexternas.  14,M.Semimembranosus.  15,  M.  Peroneus. 
(After  Jackson). 

arises.  You  should  have  a  preparation  with  bone  at  each  end. 
Suspend  the  muscles  by  clamping  one  bone  in  the  flat-jawed 
clamp.  Fasten  the  other  end  to  a  muscle  lever  to  which  a 


22  EXPERIMENTAL  PHYSIOLOGY. 

large  scale  pan  is  attached.  Obtain  a  record  of  the  comparative 
length  of  the  muscle  without  weight  and  with  weights  increasing 
by  10  gms.  at  each  trial.  The  drum  should  be  moved  by  hand 
between  each  increment.  Continue  until  the  point  of  rupture 
is  reached.  Plot  a  curve  of  these  results. 

In  a  second  preparation,  add  10  gm.  increments,  but  stop 
before  the  muscle  is  injured.     Now  remove  10  gms.  at  a  time, 
securing  a  record  in  each  case.    Plot  a  curve  of  the  recovery. 
^^          In  a  similar  manner  obtain  records  from  a  rubber  band, 
both  for  extension  and  recovery. 

Study  the  extensibility  of  a  contracted  muscle  as  compared 
to  the  same  muscle  at  rest.     Arrange  a  muscle  preparation  as 
//^.     before.     Obtain  short  records  of  the  muscle  at   rest  and  when 
stimulated  by  a  single  maximal  break  shock  without  any  weight. 
Continue  to  do  this  for   10  gram  increments  as  far  as  possible. 
What  happens  when  a  load  is  reached  which  the  muscle  cannot  lift? 
rest  and  when  stimulated  by  a  single   maximal  break  shock 
without  any  weight.     Continue  to  do  this  for  10  gram  incre- 
ments as  far  as  possible.    What  happens  when  a  load  is  reached 
which  the  muscle  cannot  lift? 

Plot  extension   curves  of   the   contracted   muscle   and   the 
resting  muscle  so  that  they  may  be  easily  compared. 

THE  SIMPLE  CONTRACTION. 

Although  muscle  seldom  responds  by  a  simple  twitch  when 
called  into  action  in  the  body,  its  behaviour  can  be  conveniently 
studied  when  it  gives  such  twitches.  Simple  contractions  can  be 
caused  by  single  electrical  stimuli.  In  order  to  observe  the  action 
of  a  single  muscle  it  is  isolated  from  its  neighbours  and  arranged  as 
described  in  the  experimental  work  so  that  when  contracting  a 
record  is  made  upon  the  surface  of  a  rapidly  rotated  cylinder 
(Fig.  5).  By  means  of  a  signal  magnet  and  a  tuning  fork  the  time 
required,  for  the  initiation  and  completion  of  the  action,  can  be 
determined.  The  time  elapsing  between  the  application  of  the 
stimulus  and  the  first  visible  contraction  is  about  0.01  sec.  for  a 
frog's  gastrocnemius.  With  the  more  quickly  responding  mirror 
method  it  is  0.0065  sec.  The  time  consumed  in  the  contraction 


VOLUNTARY  MUSCLE. 


23 


FIG.  5.  Rapid  kymograph,  (a)  Terminals  to  be  connected  in 
primary  circuit;  (&)  Movable  ring  for  second  stimulus;  (c)  Release 
which  starts  drum. 


24  EXPERIMENTAL  PHYSIOLOGY. 

averages  0.04  sec.  while  that  used  in  relaxation  is  slightly  more, 
0.05  sec..  Roughly  the  total  time  involved  in  the  various  changes 
is  0.1  sec.  for  the  frog's  gastrocnemius  (Fig.  6). 

The  duration  of  the  simple  twitch  varies  in  different  animals. 
It  is  less  in  the  rabbit,  0.07  sec.,  and  considerably  less  in  insects, 
0.003  sec. 

The  real  LATENT  PERIOD  is  primarily  due  to  the  time  consumed 
in  inducing  the  changes  in  muscle  leading  up  to  contraction.  Such 
changes  vary  with  the  onset  of  fatigue,  modification  of  temperature, 
and  intensity  of  the  stimulus.  Besides  this,  other  factors  are 
added.  If  a  load  is  attached  to  the  muscle,  the  preliminary  effect 
of  attempted  contraction  is  a  slight  elongation  on  account  of  the 
inertia  of  the  load.  With  the  ordinary  apparatus  friction  also 
slows  the  response. 


FIG.  6.     Record  of  an  isotonic  contraction  of  a  frog's  gastrocnemius  muscle. 
Stimulated  at  X.     Tuning  fork  tracing,  1/100  sec. 

Contraction  Period. — A  muscle  requires  time  for  the  develop- 
ment of  the  maximum  contraction  because  each  individual  muscle 
fibre  is  not  stimulated  in  all  parts  simultaneously,  but  receives  its 
impulse  at  the  motor  end-plate  located  near  the  middle  of  the  fibre. 
Hence  the  contraction  spreads  outward  at  the  rate  of  3  to  4  meters 
per  sec.  In  human  muscle  the  velocity  of  such  a  wave  is  10  to 
13  meters  per  sec.  Therefore,  even  though  each  muscle  fibre  of  a 
mass  may  be  stimulated  simultaneously  through  a  nerve  trunk, 
time  is  required  for  the  spread  of  the  contraction  throughout  the 
fibres. 

This  can  be  shown  experimentally  in  a  muscle  with  parallel 
fibres  such  as  the  sartorius.  Levers  are  arranged  resting  on  each 
end  of  the  muscle  so  that  when  the  corresponding  part  of  the  muscle 


VOLUNTARY  MUSCLE.  25 

contracts  a  record  will  be  made  on  a  drum.  These  levers  are  so 
adjusted  that  they  write  directly  one  above  the  other.  If  both 
parts  of  the  muscle  contracted  simultaneously  the  levers  would 
move  simultaneously.  One  end  of  the  muscle  is  stimulated  with 
a  single  shock.  That  end  contracts  some  time  before  the  other, 
as  shown  by  the  records  upon  the  kymograph.  By  measuring  the 
length  of  muscle  between  the  levers  and  determining  the  time 
with  a  tuning  fork  on  the  drum,  the  rate  in  meters  per  sec.  can  be 
ascertained. 

Relaxation  is  an  active  process  and  is  not  entirely  due  to  the 
effect  of  tension  upon  a  muscle  which  has  ceased  to  contract. 

If  a  frog's  muscle  is  carefully  isolated  and  dipped  in  olive  oil 
to  reduce  friction,  it  will  actively  relax  after  contraction,  provided 
it  is  floated  on  mercury. 

Volume  of  a  Contracting  Muscle. — The  contraction  of  a 
muscle  does  not  change  its  volume  as  the  following  experiment 
will  show. 

*Experiment  7. — Two  well  insulated  wires  from  the  secondary 
terminals  of  an  inductorium  are  passed  through  one  hole  of  a 
rubber  stopper.  The  bare  ends  of  the  wire  are  connected  to 
opposite  ends  of  a  frog's  gastrocnemius,  which  is  then  suspended 
within  a  wide-mouthed  bottle.  The  hole  through  which  the 
wires  passes  is  made  water-tight.  A  glass  tube  drawn  out  to  a 
capillary  is  inserted  in  the  other  hole  after  the  bottle  has  been 
completely  filled  with  isotonic  NaCl  solution.  The  solution 
should  extend  a  short  distance  into  the  capillary  portion  of  the 
tube.  The  inductorium  is  arranged  to  produce  a  tetanizing 
current.  In  spite  of  the  short-circuiting  through  the  solution, 
if  a  sufficiently  strong  current  is  used,  the  muscle  can  be  made 
to  contract. 

Determine  whether  or  not  any  change  in  volume  takes  place 
due  to  contraction. 

Isotonic  Contraction. — When  a  muscle  lifts  a  light  load  it 
shortens  with  little  opposition,  the  tension  remaining  nearly  con- 
stant throughout.  Such  a  contraction  is  literally  one  with  constant 
or  iso-tension,  hence  called  isotonic. 

Experiment  8.— Isotonic  Muscle  Contraction.— The  time 
elements  in  the  contraction  and  relaxation  of  a  muscle  can  best 


26  EXPERIMENTAL  PHYSIOLOGY. 

be  studied  by  obtaining  a  record  of  the  muscle  on  a  rapidly 
moving  drum.  A  gastrocnemius  preparation  in  the  moist 
chamber  is  prepared  for  direct  stimulation  by  connecting  each 
end  of  the  muscle  to  a  binding  post  (Fig.  5).  These  binding 
posts  are  connected  in  turn  to  the  terminals  of  the  secondary 
coil.  Moist  filter  paper  in  the  chamber  will  prevent  drying  of 
the  muscle. 

The  muscle  lever  must  be  in  such  a  position  that  it  will 
continue  to  write  on  the  drum  when  the  muscle  contracts. 
Weight  the  scale  pan  sufficiently  to  permit  an  appropriate 
excursion  of  the  lever.  Adjust  the  after-loading  screw  so  that 
the  resting  muscle  does  not  support  this  weight.  The  electro- 
magnetic signal  should  be  supported  on  the  same  stand  as  the 
muscle  lever  and  its  writing  point  should  be  close  to  the  writing 
point  of  the  muscle  lever,  in  line  vertically  with  it.  Always 
make  alignment  marks  on  the  drum  with  all  writing  points 
before  recording  a  muscle  contraction.  Both  the  electromag- 
netic signal  and  the  kymograph  should  be  introduced  into  the 
primary  circuit  of  the  inductorium. 

After  determining  a  suitable  strength  for  the  stimulating 
current,  record  a  contraction,  using  the  spring-driven  drum. 
By  means  of  the  lever  at  rest,  record  below  this  a  base  line. 
Now  draw  an  arc  with  the  lever  from  the  point  of  maximal 
contraction  to  the  base  line.  Obtain  a  tuning  fork  record 
between  the  base  line  and  signal  line. 

In  this  manner  secure  three  or  more  good  records.  After 
the  paper  has  been  removed  from  the  drum  and  the  surface 
fixed  with  rosin,  determine  the  time  for  the  latent  period, 
contraction  period  and  relaxation  period. 

If  you  have  time  obtain  additional  records  in  which  the 
after-loading  screw  is  changed,  so  that  the  load  is  picked  up 
earlier  or  later  than  at  first. 

Discuss  the  factors  which  might  be  involved  in  production 
of  the  latent  period. 

Experiment  8a.— Modification  for  Harvard  Kymograph.— The 
writing  point  of  the  signal  magnet  must  be  in  a  vertical  line 
with  the  writing  point  of  the  muscle  lever.  Signal  magnet  and 
muscle  lever  are  clamped  as  close  together  as  possible  on  the 


VOLUNTARY  MUSCLE.  27 

same  stand.  The  tuning  fork  with  writing  point  bent  back- 
ward is  fastened  on  a  separate  stand  at  such  a  height  that  when 
vibrating  its  record  will  come  between  that  of  the  muscle  lever 
and  signal-magnet.  The  tuning  fork  is  placed  in  the  opposite 
direction  to  that  of  the  muscle  lever  but  as  close  as  possible 
without  interference.  The  screw  at  the  top  of  the  rod  support- 
ing the  drum  is  tightened  so  that  the  drum  can  be  spun  freely 
by  hand.  Two  persons  are  required  to  perform  the  experiment. 
They  should  practice  until  they  can  perform  teamwork  without 
difficulty. 

The  muscle  and  signal-magnet  levers  are  adjusted  against 
the  surface  of  the  drum,  then  number  one  vibrates  the  tuning 
fork  and  applies  its  writing  point  to  the  drum.  Number  two 
spins  the  drum  rapidly  enough  to  show  distinctly  the  individual 
vibrations  on  the  tuning  fork,  and  as  soon  as  the  speed  is 
uniform  number  two  stimulates  the  muscle  with  a  break  shock. 
Number  one  must  be  ready  to  push  the  kymograph  away  from 
the  recording  points  as  soon  as  the  contraction  and  relaxation 
are  finished.  Directions  for  the  remainder  of  the  experiment 
are  the  same  as  in  Experiment  8. 

Isometric  Contraction. — Sometimes  a  muscle  tries  to  lift  a 
load  which  it  cannot  budge.  The  muscle  tugs  at  the  weight  with 
an  increasing  effort,  but  it  cannot  shorten,  although  the  tension 
increases  with  the  effort.  Such  a  muscle  maintains  a  constant 
length.  It  is  said  to  undergo  an  isometric  contraction. 

In  the  preceding  experiment  the  force  which  opposed  the 
contraction  of  the  muscle  was  essentially  a  constant  one,  so  that 
the  muscle  tension  remained  nearly  the  same.  In  the  present  ex- 
periment the  tension  is  made  to  increase  as  contraction  proceeds 
and  the  change  in  muscle  length  is  small.  It  is  true  that  the  muscle 
does  not  maintain  a  constant  length,  but  it  approaches  that  con- 
dition. 

*Experiment  9. — Fasten  the  femur  of  a  gastrocnemius  preparation 
in  a  flat-jawed  clamp  which  has  been  fixed  in  the  upper  part  of 
the  tripod.  Connect  the  tendon  by  a  hook  to  the  spring  lever, 
the  latter  being  supplied  with  a  writing  point.  Connect  the 
secondary  terminals  of  the  inductorium  with  the  binding  posts 
of  the  clamp  and  the  lever.  To  avoid  poor  contacts  you  should 


28  EXPERIMENTAL  PHYSIOLOGY. 

connect  the  binding  post  of  the  lever  to  the  tendon  by  means 
of  a  fine  wire. 

With  the  muscle  under  some  tension  secure  a  record  of  a 
single  contraction  upon  the  drum  of  the  spring-driven  kymo- 
graph. 

Secure  a  second  record  with  an  increase  in  tension.  Record 
an  iso tonic  curve  by  means  of  the  other  lever  on  the  tripod. 
Stimulation  signals  and  tuning  fork  records  must  be  shown 
under  each  record. 

In  order  to  obtain  the  tension  or  resistance  overcome  by  the 
muscle  in  the  isometric  contraction,  turn  the  spring  over  and 
attach  the  large  scale-pan  (weight  20  grams).  Then  add 
sufficient  weights  to  stretch  the  spring  to  the  same  extent  as 
occurred  in  the  isometric  contractions.  Turn  the  drum  by 
hand  to  make  short  abscissae.  Mark  these  lines  with  the 
weights.  (May  also  be  done  with  Harvard  kymograph  as  in 
Exp.  8a). 

Compare  the  latent  periods,  contractions  and  relaxations  in 
the  isometric  and  isotonic  records. 

It  is  never  possible  to  obtain  a  purely  isotonic  contraction,  for 
in  all  contractions  of  this  kind,  tension  does  change,  though  ever 
so  little.  Nor  does  the  purely  isometric  type  exist,  in  spite  of  the 
fact  that  the  muscle  does  not  lift  its  load  and  thus  appears  to  be 
free  from  any  shortening  of  fibres.  Watch  such  a  muscle  at  work. 
Some  of  the  fibres  do  thicken  at  least  in  part  of  their  course,  there- 
fore they  must  shorten.  They  probably  do  so  at  the  expense  of  a 
slight  extension  of  the  tendon  or  of  other  fibres. 

Throughout  the  activity  of  the  muscles  of  the  body  we  may 
have  contractions  predominantly  isotonic  or  predominantly  iso- 
metric or  these  may  be  combined  in  various  proportions. 

EFFECT  OF  TEMPERATURE  ON  CONTRACTION. 

Chemical,  changes  underlie  muscle  activity.  All  chemical  pro- 
cesses are  influenced  by  temperature,  a  rise  causing  an  increase 
in  the  rate  of  the  reaction,  a  fall  causing  a  decrease.  Within 
certain  limits  we  find  this  true  in  muscle.  There  is  this  difference 
from  inorganic  chemical  processes — the  maximum  reaction  is  soon 


VOLUNTARY  MUSCLE. 


29 


reached  in  muscle,  increase  beyond 
that  temperature  reduces  more 
and  more  the  response  of  the 
muscle  until  at  about  38°  C.  in 
the  frog  the  irritability  of  the 
muscle  is  lost.  Muscle  is  not  alone 
in  possessing  an  optimum  temper- 
ature for  its  activities.  All  tissues 
have  an  optimum  temperature. 
This  optimum  varies  iri  different 
individual  animals,  especially  cold- 
blooded animals  like  the  frog. 
Winter  frogs  possess  a  lower 
optimum  than  summer  frogs. 

Not  only  is  the  height  of  con- 
traction changed  by  temperature 
rise  or  fall,  but  the  duration  of  its 
phases  is  changed  as  well.  At  low 
temperatures  the  latent  period  and 
duration  of  the  contraction  may 
be  several  times  the  corresponding 
stages  at  higher  temperatures 
(Fig.  7). 

Mammals  differ  from  frogs  in 
maintaining  a  more  or  less 
optimum  temperature  for  their 
tissues  independent  of  external 
changes. 

Experiment  10.*— Fasten,  by 
means  of  thread  or  fine  wire, 
the  femur  of  a  gastrocnemius 
preparation  to  the  short  arm 
of  the  L-shaped  glass  rod  which 
has  previously  been  fixed  by 
its  long  arm  in  the  flat-jawed 
clamp  (Fig.  8).  Connect  the 
tendon  by  means  of  a  fine  wire 
to  the  pulley  of  the  muscle 
lever,  suitably  weighted.  Con- 

*This  experiment  may  be  done  with  the  Har- 
vard kymograph  using  the  highest  speed  of  the 
clockwork. 


&S, 

w  S 


- 


«- 

o.2 

II* 


30 


EXPERIMENTAL  PHYSIOLOGY. 


nect  the   secondary    terminals   of  the   inductorium    with    the 
muscle    lever    and    with    the    femur.      On    a    rapidly    moving 


surface  secure  records  of  twitches  immediately  after  the  muscle 
has  been  immersed  in  isotonic  salt  solution  at  the  following 
temperatures,  each  for  three  minutes:  4°  C.,  10°  C.,  15°  C., 
25°  C.,  30°  C.,  35°  C.,  and  40°  C.  Use  the  same 


VOLUNTARY  MUSCLE.  31 

strength  of  stimulus  in  each  case  and  superimpose  the  records, 
taking  care  always  to  start  at  the  same  point  on  the  drum. 
A  tuning  fork  record  is  made  and  the  latent  period  is  also 
shown  by  the  signal  magnet. 

Discuss  the  variations  in  rate  and  magnitude  of  the  phases 
of  the  single  contractions  at  the  different  temperatures. 

Since  the  temperature  of  cold-blooded  animals  depends 
upon  the  temperature  of  the  surrounding  medium,  it  is  much 
more  variable  than  that  of  the  warm-blooded  animal.  What- 
ever can  be  said  regarding  an  optimum  temperature  for  frog's 
muscle  can  be  applied  in  a  modified  form-to  mammalian  muscle. 
The  latter,  however,  is  scarcely  ever  subjected  to  as  great  a  range 
of  temperature  and  the  optimum  is  higher. 

If  one  goes  beyond  the  temperature  at  which  the  muscle 
remains  irritable  certain  changes  will  take  place  due  to  irre- 
versible modifications  in  the  muscle  cells.  The  shortening 
of  the  muscle  fibre  due  to  coagulation  of  the  muscle  proteins 
can  be  shown  by  securing  a  record,  upon  a  very  slowly  moving 
drum,  of  the  effect  of  a  gradual  increase  of  temperature.  De- 
scribe the  appearance  of  a  muscle  so  treated. 

Chemical  changes  can  also  be  shown  by  comparing  the 
reaction  to  litmus  paper  of  the  cut  surface  of  the  muscle  with 
that  of  a  fresh  muscle. 

LOAD  AND  WORK. 

The  amount  of  work  which  a  muscle  can  do  depends  upon  the 
load  which  it  carries.    If  a  load  is  light  the  muscle  does  not  accom- 
plish a  great  deal,  even  though  it  contracts  to  its  full  extent.     On 
the  other  hand  too  great  a  load  overtaxes  the  muscle  so  that  the 
load  can  scarcely  be  lifted  and  thus  little  work  performed.    There 
is  then  for  every  muscle  an  optimum  load.    With  this  the  muscle 
is  able  to  do  the  greatest  amount  of  work  at  each  contraction. 
Experiment    11. — Arrange   for   direct   stimulation    of   a   gastro- 
cnemius  muscle  fastened  to  the  lever  of  the  tripod.     Adjust 
the  after-loading  screw  so  that  the  muscle  picks  up  the  load  in 
the  large  scale  pan  as  it  starts  to  contract.    Choose  a  stimulus 
which  is  approximately  maximal.    The  records  are  to  be  super- 


32  EXPERIMENTAL  PHYSIOLOGY. 

imposed  upon  a  rapid  kymograph,  so  that  after  once  starting 
to  record  contractions,  do  not  move  the  relative  position  of 
the  apparatus.  A  signal  magnet  is  used  to  indicate  the 
latent  period.  One  tuning  fork  record  does  for  the  whole  set. 
Using  increments  of  ten  or  twenty  grams,  depending  upon  the 
size  of  the  muscle,  increase  the  load  until  the  muscle  can  no 
longer  lift  it.  Obtain  a  record  at  each  increase  in  the  load. 

Compare  the  latent  period,  contraction  period  and  relaxation 
period  as  the  load  increases. 

Calculate  the  work  done  in  gram-millimeters  at  each  con- 
traction by  multiplying  the  load  by  the  vertical  distance 
through  which  the  load  was  moved.  The  latter  is  to  be  deter- 
mined by  dividing  the  height  of  contraction  as  recorded  on 
the  drum  by  the  magnification  of  the  lever.  Now  plot  a  curve 
of  work  and  load,  with  work  as  ordinate  and  load  as  abscissa.. 

What  is  the  relation  of  the  magnitude  of  the  load  to  the  work 
accomplished? 

INFLUENCE  OF  VERATRINE  UPON  CONTRACTION. 

It  is  possible  with  certain  drugs  to  affect  one  phase  of  the  con- 
traction in  a  muscle  without  materially  modifying  the  other. 
Veratrine  and  to  some  extent  glycerol  and  nicotine  produce  this 
effect. 

*Experiment  12. — Prepare  one  gastrocnemius  muscle  of  a  frog 
without  injury  to  the  circulation  of  the  other  gastrocnemius. 
Inject  a  few  drops  of  0.1%  veratrine  acetate  solution  into  the 
dorsal  lymph  sac  of  the  frog  as  soon  as  the  first  muscle  has  been 
prepared  and  removed  so  that  the  other  gastrocnemius  may  get 
a  sufficient  amount  of  the  drug  by  the  time  that  it  is  wanted. 
Secure  a  record  of  the  contraction  of  the  muscle  first  pre- 
pared, using  the  spring-driven  kymograph.  Now  prepare  the 
second  gastrocnemius  and  obtain  a  contraction  in  a  similar 
fashion.  From  time  to  time  take  other  records  to  discover 
when  the  veratrine  effect  disappears. 

Compare  the  contractions  of  the  normal  and  veratrinized 
muscles. 


VOLUNTARY  MUSCLE.  33 

FATIGUE.  —M^— 

It  is  well  known  that  excessive  WEBSRl  SBSBB 
use  of  a  muscle  reduces  its  efficiency.  j^SSSSl  rW^JrltinB 
In  fact  all  phases  of  contraction  are 
affected.  A  careful  study  of  the  sub- 
ject shows  the  following  changes. 
Repeated  contraction  at  first  causes  an 
increase  in  response,  called  the  "stair- 
case" or  "treppe"  effect.  A  maximum 
is  soon  reached  and  persists  for  a  time. 
Then  the  contractions  gradually  de- 
crease in  magnitude  until  a  point  is 
reached  where  the  muscle  fails  to  re- 
spond (Fig.  9).  In  the  latter  stage 

of  fatigue  the  muscle  may  fail  to  relax  •nnMiiiiHiiiMiiiifc  •jiii 
entirely  between  twitches  so  that  it  ^^^K'r/iIWi  !K**iBim 
persists  in  a  state  of  "contracture." 

It  has  been  shown  that  certain 
substances  are  produced  during 
muscular  activity  such  as  carbon- 
dioxide,  mono-potassium  phosphate 
and  para-lactic  acid.  If  these  sub- 
stances are  injected  into  a  fresh 
muscle  the  first  effect  is  to  augment 
the  contractile  response.  Injection 
of  larger  amounts  reverses  the  effect 
so  that  the  response  is  reduced.  In 

other  words  it  is  possible  to  induce  in      MD  i|BIIDS*SW^ 
a  fresh  muscle  the  various  stages  of     HHf !»HlSB«iiJHsl 
excitability  and  fatigue  by  means  of 
the    waste    substances    produced    in      BBl  IIISSIIB^^SB 
muscle,    the  effect    depending    upon          HiiilliUll 
the    quantity    of    these    substances. 
These  observations  lead  one  to  con- 
clude that  the  accumulation  of  waste  IkVXV 

^•k'vNt^H^SiKl  ^  u 

substances    in    a    muscle   is   a   large     BBHfci  T' iBSit Wl 


factor  in  producing  these  conditions. 
This  is  further  substantiated  by  the 
fact  that  increasing  the  circulation  to 


1  1 


34  EXPERIMENTAL  PHYSIOLOGY. 

a  muscle  delays  the  onset  of  fatigue  and  prolongs  the   staircase 
effect. 

In  frog's  muscle  fatigue  is  accompanied  by  a  lengthening  of 
the  time  for  contraction  and  relaxation,  while  in  mammalian 
muscle  the  contractions  merely  become  shorter,  with  little  effect 
upon  the  duration.  The  using-up  of  materials  stored  in  muscle 
also  contributes  to  fatigue,  for  in  starvation  fatigue  is  induced 
more  readily  while  the  feeding  of  glucose  helps  to  prevent  it. 

Effect  of  Fatigue  upon  Contraction. — Fatigue  is  partially 
due  to  the  accumulation  of  waste  substances,  therefore  any  re- 
duction in  the  circulation  will  hasten  its  onset.  In  the  ordinary 
muscle  preparation  which  has  been  removed  from  the  circulation, 
fatigue  develops  quickly  and  is  easily  studied. 

Experiment  13. — Pith  the  brain  of  a  frog  taking  care  to  cause  as 
little  bleeding  as  possible.  Make  a  small  incision  in  the  skin 
of  the  heels  and  free  the  gastrocnemius  tendons  from  the  ankles. 
Do  not  skin  the  legs.  Fasten  the  frog  to  the  frog  board  so  that 
the  knees  are  held  firmly,  but  the  circulation  to  the  lower  legs  is 
not  occluded.  This  may  be  done  by  passing  a  hook  through  the 
ligaments  on  the  convexity  of  the  knee.  Occlude  the  circula- 
tion in  the  right  leg  by  tying  a  mass  ligature  about  the  thigh 
and  connect  the  tendon  of  the  right  leg  by  means  of  a 
thread  to  a  lever  arranged  to  record  contractions  of  the 
gastrocnemius.  Connect  one  terminal  of  the  secondary  coil 
to  the  tendon  with  a  piece  of  the  wire;  connect  the  other 
terminal  to  a  wire  looped  about  the  knee.  Arrange  to 
stimulate  with  maximal  make  and  break  shocks.  Adjust 
the  after-loading  screw  and  load  the  muscle  with  30 
grams.  Because  the  first  few  contractions  illustrate  important 
phenomena,  do  not  stimulate  the  muscle  until  ready  to  record 
the  series  of  contractions  resulting  in  fatigue. 

Start  the  kymograph  revolving  slowly  and  stimulate  as 
uniformly  as  possible  with  alternating  make  and  break  shocks 
at  second  intervals  until  the  muscles  cease  to  respond.  Allow  the 
muscle  to  rest  five  minutes  and  record  a  second  fatigue  tracing. 
The  record  should  illustrate  the  phenomena  of  (1)  Treppe, 
(2)  Fatigue,  (3)  Contracture.  How  do  you  explain  Treppe  and 
Fatigue  in  terms  of  the  All  or  None  law?  What  change  in  the 
behaviour  of  the  muscle  is  responsible  for  contracture? 


VOLUNTARY  MUSCLE.  35 

Repeat  the  experiment  using  the  gastrocnemius  of  the  left 
leg,  the  circulation  of  which  is  not  disturbed.  Compare  Treppe, 
Fatigue,  Contracture  and  Rest  in  the  circulated  and  non- 
circulated  muscle.  The  circulated  muscle  may  reach  a  point 
beyond  which  fatigue  fails  to  develop  further.  This  is  the 
fatigue  level.  Explain  why  this  occurs.  Alter  the  rate  of 
stimulation  and  explain  its  effect  on  the  height  of  the  fatigue 
level. 


FIG.  10.  Graphic  record  of  two  voluntary  contractions  showing  their  tetanic  nature.  Made 
by  pull  of  the  index  finger  against  a  stiff  spring  at  the  end  of  which  a  writing  point  is  attached. 

TETANUS. 

Voluntary  muscular  action  is  caused  by  a  rapid  succession  of 
impulses  travelling  outward  along  a  motor  nerve.  The  muscle 
therefore  does  not  respond  by  a  simple  twitch,  but  by  a  more  or  less 
sustained  contraction.  Even  the  quickest  voluntary  movements 
are  a  fusion  of  several  simple  contractions. 

Several  proofs  have  been  obtained  of  the  composite  nature  of 
such  contraction.  First  it  has  been  found  by  the  use  of  a  sensitive 
galvanometer  that  several  impulses  pass  along  a  nerve  which  is 
exciting  a  muscle  even  to  brief  contraction. 

Second,  a  sound  can  be  heard  through  a  stethoscope  applied 
to  a  muscle  contracting  voluntarily.  This  sound  is  no  doubt  due 


36  EXPERIMENTAL  PHYSIOLOGY. 

to  vibrations  produced  by  the  rapidly  contracting  muscle.  The 
sound  heard  is  usually  an  overtone  because  the  actual  vibration 
rate  is  near  the  lower  limit  of  audibility. 

Third,  a  magnified  record  obtained  by  means  of  a  lever,  of  a 
muscle,  under  sustained  voluntary  contraction,  is  not  perfectly 
smooth,  but  contains  many  fine  regularly  occurring  contractions 
superimposed  upon  the  mam  contraction  (Fig.  10). 


FIG.  11.  The  effects  of  successive  stimuli  on  skeletal  muscle  and 
cardiac  muscle.  The  vertical  marks  show  where  stimuli  were  introduced. 
Tracings  at  bottom  are  the  result  of  stimuli  sufficiently  close  together  to  pro- 
duce tetanus.  Notice  that  the  heart  shows  neither  summation  nor  tetanus. 
(Compiled  from  tracings  published  by  T.  G.  Brodie  and  Leonard  Hill). 

Finally,  in  order  to  produce  a  sustained  artificially  stimulated 
contraction  resembling  a  voluntary  contraction,  it  is  necessary  to 
send  into  the  muscle  a  rapid  succession  of  stimuli.  Such  a  con- 
traction is  called  tetanus. 


VOLUNTARY  MUSCLE.  37 

Summation. — If  two  stimuli  are  sent  into  a  muscle  in  close 
succession  so  that  the  muscle  has  not  completely  relaxed  before 
the  second   stimulus   is  effective,   the   latter   contraction  will   be 
higher  than  the  first.     The  second  contraction  adds  its  effect  to 
that  of  the  first,  therefore  the  greatest  summation  will  occur  when 
the  second  stimulus  is  effective  during  the  greatest  height  of  the 
first   contraction    (Fig.    11).      A    certain    amount   of   summation 
results  even  though  a  maximal  stimulus  is  used.    A  series  of  rapidly 
repeated  stimuli  on  account  of  the  summation  effects,  will  cause  a 
much  higher  contraction  than  is  obtained  from  a  single  stimulus. 
Analysis  of  Tetanus. — Voluntary  muscle  contraction  is  really 
a  series  of  twitches  occurring  so  rapidly  that  relaxation  is  incom- 
plete or  fails  to  develop.     This  action  can  be  analyzed  best  by  a 
study  of  two  simple  twitches  occurring  close  together. 
Experiment   14. — Arrange  a  muscle  in  the  moist  chamber  for 
stimulation    by    the    inductorium.      Set   an   electro-magnetic 
signal  close  to  and  in  line  with  the  writing  point  of  the  muscle 
lever.    Connect  the  signal  and  the  kymograph  in  the  primary 
circuit.    Adjust  both  contacts  upon  the  disk  of  the  kymograph 
so  that  two  stimuli  are  sent  into  the  muscle  with  each  revolu- 
tion of  the  drum.    With  the  contacts  far  apart  obtain  a  record 
of  the  twitches  when  the  drum  is  released.     Make  a  series  of 
records  in  which  the  stimuli  are  closer  and  closer  together,  by 
adjusting   the   sliding   contact.      Continue   this   series   to   the 
point  of  complete  summation. 

In  order  to  observe  the  effect  of  more  than  two  successive 
stimuli,  replace  the  kymograph  by  the  wheel  interrupter  in 
the  circuit.  Make  records  on  a  slower  drum,  turning  the  inter- 
rupter at  different  rates.  With  each  new  trial  increase  the  rate 
until  complete  fusion  is  obtained. 

Next  replace  the  wheel  interrupter  by  the  vibrating  spring 
on  the  inductorium.  In  this  way  tetanus  can  be  produced 
automatically. 

Discuss  summation  and  the  development  of  tetanus. 
In  order  to  perform  this  experiment  with  the  Harvard  Kymo- 
graph use  the  highest  speed.     A  key  is  placed  in  the  primary 
circuit  but  one  of  the  wires  is  connected  to  a  dissecting  needle. 
Stimulation  is  obtained  by  quickly  snapping  the  needle  over  one 


38  EXPERIMENTAL  PHYSIOLOGY. 

edge  of  the  binding  post  on  the  key.  This  can  be  done  so  quickly 
that  one  shock  is  effective.  Follow  directions  as  in  the  original 
description. 

RED  AND  PALE  MUSCLE  FIBRES. 

Voluntary  muscle  fibres  may  be  of  two  kinds,  one  pale  in  aspect, 
the  other  red.  The  red  fibres  are  thinner  and  possess  a  larger 
amount  of  sarcoplasm.  They  possess  a  greater  number  of  nuclei 
and  a  larger  blood  supply.  Many  of  the  capillaries  to  red  fibres 
are  furnished  with  dilatations. 

Red  fibres  contract  more  slowly  and  fatigue  less  readily  than 
do  pale  fibres.  The  former  appear  to  be  adapted  for  heavy  work, 
while  the  latter  are  for  rapidity  of  action. 

Some  muscles  are  composed  largely  of  red  fibers,  such  as  the 
soleus  in  the  rabbit.  The  gastrocnemius  on  the  other  hand  con- 
tains mostly  pale  fibres.  Quite  often  both  types  of  fibres  are 
present  in  a  muscle,  but  one  predominating. 

HEAT  PRODUCTION. 

A  muscle  releases  a  considerable  amount  of  energy  in  the  form 
of  heat  when  it  contracts.  Everyone  is  familiar  with  the  increased 
amount  of  heat  after  vigorous  exercise.  Sustained  contraction  in  a 
large  muscle  may  raise  the  temperature  1°  C.  or  more,  but  due  to 
the  circulation  and  the  control  mechanism,  excess  heat  is  distributed 
and  eventually  lost. 

It  has  been  estimated  that  CO  to  75  per  cent,  of  the  energy  used 
in  contraction  produces  heat,  the  balance  being  converted  into 
work.  Unpractised  movements  result  in  a  greater  proportion  of 
heat  production.  Training,  therefore,  is  highly  important  in 
getting  the  greatest  work  from  a  muscle. 

There  are  two  stages  of  heat  production.  The  first  is  immedi- 
ate or  "explosive"  in  character  and  will  take  place  in  the  absence 
of  free  oxygen.  For  example,  a  muscle  which  contracts  in  Ringer's 
solution  from  which  free  oxygen  has  been  removed  or  in  nitrogen, 
releases  heat  of  the  first  stage.  The  second  stage  develops  slowly 
and  is  postponed  if  oxygen  is  absent.  The  evolution  of  heat  in 
this  stage  continues  for  a  long  time  after  the  mechanical  response. 
The  amount  of  heat  evolved  is  as  great  as  that  of  the  first  stage. 


VOLUNTARY  MUSCLE.  39 

RIGOR  MORTIS. 

Within  a  few  hours  after  an  animal  dies,  its  muscles  undergo  a 
pronounced  irreversible  change.  They  contract  and  lose  their 
extensibility.  The  contraction  is  not  vigorous  as  can  be  shown  by 
resisting  it  with  slight  tension. 

The  chemical  changes  which  seem  to  underlie  the  process,  are 
the  production  of  carbon  dioxide  and  lactic  acid,  which  by  causing 
coagulation  of  the  muscle  proteins,  myosinogen  and  paramyosingen, 
bring  about  the  contraction.  Incomplete  oxidation  seems  to  favour 
the  development  of  rigor,  for  if  plenty  of  oxygen  is  supplied  neither 
rigor  mortis  nor  lactic  acid  is  present. 

Heat  is  also  produced  as  rigidity  comes  on,  which  accounts  for 
the  warmth  which  may  be  noticed  sometimes  hours  after  death. 

Rigor  mortis  being  due  to  chemical  changes,  anything  which 
hastens  these  causes  an  earlier  development  of  the  condition. 
Thus  the  onset  is  much  earlier  at  high  temperatures;  low  tempera- 
tures, conversely,  postpone.  Fatigue,  by  speeding  up  the  produc- 
tion of  lactic  acid  and  other  substances,  causes  an  earlier  appear- 
ance of  rigor. 

This  coagulation  of  the  muscle  in  rigor  mortis  may  last  for  two 
or  three  days,  when  it  is  terminated  by  autoly  — 

Coagulation  of  muscle  proteins  may  be  caused  by  heat.  If  a 
muscle  is  gradually  heated  two  stages  are  found  to  be  present  in 
the  development  of  rigor,  the  first  at  39°  C.  in  the  frog  and  47°  C. 
in  the  mammal,  the  second  at  50°  C.  in  the  frog  and  62°  C.  in  the 
mammal.  The  first  is  due  to  the  muscle  proteins  proper  and  the 
second  to  the  connective  tissue  substances. 

Heat  rigor  is  more  complete  and  does  not  disappear  when  auto- 
lysis  supervenes. 

Similarly,  clotting  of  the  muscle  proteins  may  be  produced  by 
alcohol,  chloroform  or  other  substances. 

ELECTRICAL  CHANGES  IN  MUSCLE. 

Electrical  changes  accompany  the  contraction  of  muscle.  This 
can  be  shown  by  connecting  a  sensitive  galvanometer  to  a  muscle 
which  is  caused  to  contract  voluntarily  or  through  artificial  stimu- 
lation. A  wave  of  negative  variation  travels  from  the  point 


40  EXPERIMENTAL  PHYSIOLOGY. 

stimulated,  whether  it  be  the  motor  end  plate  or  one  end  of  the 
fibre  in  contact  with  stimulating  electrodes.  All  other  parts  of 
the  muscle  are  positive  in  relation  to  this  wave.  Suppose  as  in 
Fig.  12  the  galvanometer  G  is  connected  to  the  muscle  at  2  and 
3  and  the  stimulating  electrodes  are  at  1.  A  single  contraction  is 
initiated  at  1.  This  contraction  is  preceded  by  a  negative  electrical 
condition  which  first  reaches  2  (A),  at  that  moment  2  will  be 
negative  in  relation  to  3,  causing  a  deflection  of  the  galvanometer. 
The  wave  continues  to  move  onward,  quickly  passing  2  and  soon 
reaching  3.  When  3  is  reached  (B)  it  will  become  negative  to  2. 
There  will  therefore  be  a  reversal  of  the  galvanometer.  The  gal- 
vanometer moves  first  in  one  direction  and  then  in  the  other.  This 
is  called  a  diphasic  variation.  The  electrical  change  attending  the 
contraction  of  muscle  is  designated  the  ACTION  CURRENT. 

When  a  muscle  is  cut  or  injured,  that  particular  region  becomes 
electronegative  to  other  parts  of  the  muscle  which  are  uninjured. 
If  connected  by  a  conductor  a  slight  current  will  be  set  up,  called 

the  CURRENT  OF  INJURY. 


FIG.  12.  Diagram  to  show  the  passage  of  an  electrical  change  over  muscle.  When 
a  muscle  is  stimulated  at  one  end  (i)  a  negative  electrical  change  is  started,  passing 
along  the  muscle,  just  preceding  the  contraction.  A  galvanometer  (G)  is  connected 
with  the  muscle  by  two  leading  off  electrodes,  2  and  3.  As  the  negative  change  reaches 
2  (A)  the  current  will  pass  through  the  galvanometer  from  3  to  2.  But  when  the 
negative  variation  reaches  3  (B)  the  current  is  reversed.  This  is  called  the  diphasic 
variation. 

THE  NERVE-MUSCLE  AS  A  RHEOSCOPE. 

The  electrical  changes  set  up  in  muscle  can  be  detected  by  a 
vigorous  nerve-muscle  preparation.  The  nerve  is  permitted  to 
touch  the  muscle  at  a  negative  region  and  a  positive  region.  In 
a  freshly  cut  muscle  at  the  time  of  making  the  second  contact, 
the  rheoscopic  muscle  will  twitch.  In  a  muscle  stimulated  through 
its  nerve  the  rheoscopic  muscle  will  twitch  at  each  twitch  of  the 


VOLUNTARY  MUSCLE  41 

tested  muscle.  The  explanation  is  that  the  electrical  changes 
in  the  tested  muscle  are  strong  enough  to  initiate  impulses  in  the 
nerve  of  the  rheoscopic  preparation.  However,  due  to  the  poor 
condition  of  the  rheoscopic  nerve-muscle,  the  experiment  frequently 
fails. 

The  sciatic-gastrocnemius  preparation  to  be  used  as  a  rheoscope 
should  be  taken  from  a  very  healthy  frog  and  dissected  out  with 
the  greatest  care.  Abuse  of  the  nerve  may  destroy  its  sensitiveness 
so  that  a  new  preparation  must  be  made. 

Experiment  15.— Current  of  Injury.— One  end  of  a  gastroc- 
nemius  muscle  is  cut  across  transversely.  This  and  the  rheo- 
scopic preparation  are  placed  side  by  side  on  a  clean  glass  plate. 
The  rheoscopic  nerve,  near  its  muscle,  is  placed  in  contact  with 
the  uninjured  surface  of  the  muscle  to  be  tested,  the  rest  of  the 
nerve  being  held  apart  by  means  of  a  glass  hook.  Now  the  tip 
of  the  rheoscopic  nerve  is  allowed  to  touch  the  injured  surface 
of  the  muscle  to  be  tested.  A  contraction  of  the  rheoscopic 
muscle  should  result  at  the  moment  of  the  nerve's  contact  with 
the  injured  surface. 

Current  of  Action. — Two  nerve-muscle  preparations  are  laid 
side  by  side  on  a  glass  plate.  The  nerve  of  the  one  which  is  to 
serve  as  the  rheoscope  is  placed  lengthwise  against  the  muscle 
to  be  tested  and  is  then  lifted  by  a  glass  rod  at  its  middle  so 
that  it  is  in  contact  with  the  muscle  only  at  both  ends.  The 
nerve  of  the  muscle  to  be  treated  is  next  stimulated  by  single 
shocks.  With  each  twitch  the  rheoscopic  muscle  should  re- 
spond. If  the  test  muscle  is  tetanized,  the  rheoscopic  muscle 
should  be  tetanized. 

A  secondary  twitch  can  also  be  obtained  by  laying  a  freshly 
prepared  nerve  upon  a  beating  frog  heart.  The  two  regions  of 
contact  for  the  nerves  are  the  base  and  the  apex,  the  middle 
part  of  the  nerve  being  held  away  from  the  contracting  muscle 
as  before.  Each  beat  should,  produce  a  twitch  of  the  gastroc- 
nemius. 


CHAPTER  III. 

SMOOTH  MUSCLE  AND  CILIATED  CELLS. 
SMOOTH  MUSCLE. 

There  are  two  types  of  muscle  which  are  independent  of  volun- 
tary action,  cardiac  muscle  which  is  striated  and  smooth  muscle 
which  lacks  transverse  striations.  Smooth  muscle  fibres  are 
elongated  and  pointed  at  both  ends.  They  are  generally  collected 
into  bundles.  These  bundles  are  attached  at  their  ends  to  the 
membranous  parts  where  they  occur. 

The  importance  of  plain  or  smooth  muscle  will  be  realized  when 
its  wide  distribution  is  considered.  It  is  found  in  the  lower  half 
of  the  gullet,  the  stomach,  and  intestines.  In  the  alimentary  canal 
it  occurs  not  only  in  the  muscular  coat,  but  as  a  layer  in  the  mucous 
membrane  and  in  the  villi.  It  is  present  likewise  in  the  trachea, 
bronchial  tubes,  bladder,  ureters,  uterus,  glandular  ducts,  genital 
organs,  spleen,  ciliary  muscle  and  iris.  The  contractile  element  in 
blood  vessels  consists  of  plain  muscle.  Thus  it  is  by  means  of 
smooth  muscle  that  blood  is  shifted  from  one  part  to  another  and 
emergencies  are  met.  This  adjustment  is  controlled  largely  through 
the  nervous  system. 

Movements  of  the  alimentary  canal,  mixing  of  the  digestive 
fluids  with  the  food  and  onward  propulsion  of  the  contents,  are 
brought  about  by  smooth  muscle.  Its  function  in  regulating  blood 
supply  and  the  mechanics  of  digestion  are  alone  sufficient  to 
demonstrate  its  necessity  in  the  organism. 

Extensibility  and  Elasticity. — -The  extensibility  and  elas- 
ticity are  similar  to  those  properties  in  striated  muscle.  However 
in  the  stomach,  bladder  and  uterus  the  extensibility  is  much  greater. 
The  capacity  of  these  organs  depends  upon  the  power  of  extension, 
for  when  empty  they  are  contracted  to  a  small  size. 

Irritability. — Electrical  stimulation  is  relatively  ineffective 

42 


SMOOTH  MUSCLE.  43 

with  plain  muscle,  strong  currents  being  required.  Induction 
shocks  are  less  effective  than  galvanic. 

Mechanical  stimulation  in  the  form  of  stretching  is  by  far  the 
most  adequate  form  of  stimulus,  at  least  among  artificial  stimuli. 

Contraction. — The  LATENT  PERIOD  for  smooth  muscle  response 
may  be  as  much  as  one  hundred  to  five  hundred  times  that  of 
striated  muscle.  In  the  frog's  stomach  it  is  from  one  to  ten  seconds; 
for  the  cat's  bladder,  0.25  sec.,  and  for  vascular  muscles,  0.3  to 
0.5  sec. 

The  CONTRACTION  PERIOD  may  be  as  much  as  15  to  20  seconds 
for  the  frog's  stomach.  The  amount  and  duration  of  the  con- 
traction depends  upon  the  stimulus.  In  the  frog's  stomach  a 
single  contraction  may  decrease  the  stomach  by  45%,  while  tetanus 
may  reduce  it  59%.  Although  the  contraction  may  be  large,  it  is 
much  gentler  than  that  of  voluntary  muscle. 

RELAXATION  PERIOD. — -The  time  consumed  in  relaxation  is  much 
longer  than  that  for  contraction.  In  the  frog's  stomach  it  is  said 
to  be  from  60  to  80  sec. 

Summation  and  Tetanus. — Two  successive  stimuli  properly 
spaced  will  cause  summation.  A  series  of  stimuli  will  cause  tetanus. 
To  do  this  they  need  not  be  very  frequent.  A  stimulus  every  five 
seconds  is  sufficient  in  the  frog's  stomach. 

Tone. — Smooth  muscle  possesses  the  power  of  remaining  in  a 
condition  of  persistent  shortening  for  long  periods.  Thus  hollow 
viscera  can  adapt  themselves  to  their  contents.  Tone  can  be 
varied  in  different  ways.  Cooling  increases  it,  while  heat  decreases 
it.  The  most  important  means  of  controlling  tone  seems  to  be 
through  the  extrinsic  nerve  supply,  e.g.,  stimulation  of  the  vagus 
increases  stomach  tone,  cutting  the  vagus  produces  flabbiness  in 
the  same  organ .  Throughout  life  the  walls  of  the  arteries  resist  a  high 
pressure,  this  resistance  being  controlled  by  the  nervous  system. 

Rhythmicity. — Smooth  muscle  in  certain  parts  of  the  body 
is  able  to  undergo  rhythmical  contraction.  These  are  the  alimen- 
tary canal,  ureter,  bladder,  spleen  and  blood  vessels.  In  the  sto- 
mach and  intestine  rhythmical  activity  is  induced  by  tension.  The 
rate  of  these  contractions  is  somewhat  as  follows:  stomach,  3  per 
min.,  intestine  12  per  min.,  spleen,  1  per  min. 

In  this  connection  it  is  important  to  make  it  clear  that  these 


44  EXPERIMENTAL  PHYSIOLOGY. 

rhythmic  movements  are  superimposed  upon  whatever  condition 

of  tone  prevails. 

The  intrinsic  nerve  supply  seems  to  preside  over  rhythmicity. 

Experiment  16.  —  Contraction  of  Smooth  Muscle.  —  An  L- 
shaped  glass  rod  is  fastened  by  a  clamp  so  that  it  can  be  used 
to  support  a  piece  of  intestine  about  2  cm.  long  in  a  small  beaker 
of  Ringer's  solution.  The  latter  is  maintained  at  a  tempera- 
ture of  37-38°  C.  by  immersing  the  beaker  in  a  large  tin  cup 
used  as  a  water-bath.  Air  is  allowed  to  bubble  slowly  through 
the  Ringer's  or  Locke's  solution1  by  fixing  a  small  glass  tube, 
connecting  with  the  compressed  air  supply,  so  that  its  opening 
is  near  the  bottom  of  the  beaker.  When  all  is  ready  one  end 
of  a  piece  of  intestine,  cut  from  a  rabbit  which  has  just  been 
killed,2  is  attached  to  the  hook  of  the  glass  rod  and  the  other 
to  a  heart-lever  which  is  arranged  to  record  on  a  slowly-moving 
drum.  Contractions  of  the  longitudinal  muscle  will  produce 
movement  of  the  lever. 

After  recording  several  normal  contractions  try  the  effect 
of  temporarily  reducing  the  air  supply.  Later  allow  the  tem- 
perature of  the  Ringer's  fluid  to  fall  to  that  of  the  room  and  note 
the  changes  in  tone  and  rhythmic  contractions.  Finally  study 
the  effect  of  stimulation  by  electricity.  When  ready  to  stimu- 
late remove  the  Ringer's  solution  for  a  short  time  in  order  to 
prevent  short  circuiting.  Try  make  and  break,  direct  and 
indirect  currents.  Later  attempt  to  tetanize  the  segment. 
On  account  of  the  long  latent  period  do  not  run  the  stimuli  too 
close  together  when  single  shocks  are  used. 

Observe  the  direction  in  which  a  contraction  travels  when  a 
piece  of  intestine  is  pinched  with  forceps.  In  order  to  remember 
which  is  the  oral  end  a  ligature  should  be  tied  around  that  end 
when  the  segment  is  removed.  Do  the  contractions  always 
move  in  the  same  direction  from  mechanical  stimulation?  Is 
this  type  of  stimulus  more  or  less  adequate  than  the  electrical? 


water  with  which  these  solutions  is  made  up  must  be  pure  distilled.  It 
has  been  our  experience  in  this  laboratory  that  chlorinated  lake  water  cannot  be 
used  to  distil  from.  We  are  compelled  to  use  spring  water  from  which  to  pre- 
pare the  distilled  water. 

2The   intestine,  after  removal  from  the  rabbit,  is  preserved  in  cold  Locke's 
solution  through  which  oxygen  or  air  is  occasionally  bubbled. 


SMOOTH  MUSCLE  45 

CILIATED  CELLS. 

In  addition  to  the  muscular  tissue  of  the  body  there  are  other 

contractile  elements,  viz.,  ciliated  cells. 

The  function  of  ciliated  cells  is  to  remove  mucous  and  foreign 

bodies  from  passages.     They  are  therefore  found  in  the  mucous 

membranes  of  the  trachea,  larynx,  bronchi,  nos.e,  lachrymal  duct, 

uterus,  Fallopian  tubes,  tubules  of  the  epididymis,  Eustachian  tubes 

and  middle  ear. 

Each  cell  may  have  one  or  more  cilia.    Not  only  the  cilia  of  the 

same   cell,   but   those  of  neighbouring  cells,   move   in   a  definite 

sequence,  so  that  there  is  co-ordination. 

The  power  of  these  cilia  acting  together  is  considerable.     It  is 

estimated  that  the  cilia  on  1  sq.  cm.  of  the  frog's  oesophagus  cap 

move  a  weight  of  more  than  300  grams. 

Warmth  increases  the  activity  of  cilia;  cold  decreases  it.    Drugs 

also  influence  their  movement. 

Experiment  17. — Ciliary  Action. — Remove  the  lower  jaw  of  a 
frog  and  slit  the  oesophagus.  Spread  open  the  oesophagus  with 
pins.  Determine  the  time  required  for  a  bit  of  cork  placed 
on  the  roof  of  the  mouth  to  be  moved  one  centimeter  down  the 
gullet.  Keep  the  mucous  membrane  moistened  with  salt  solu- 
tion. Pour  iso tonic  NaCl  solution,  warmed  to  30°  C.  over 
the  membrane,  drain  it  off,  then  determine  the  rate  of  move- 
ment of  a  bit  of  cork.  After  a  time  blow  ether  vapour  over  the 
membrane  and  again  determine  the  rate  of  ciliary  action. 


CHAPTER    IV. 
PHYSIOLOGY  OF  NERVE. 

All  protoplasm  possesses  the  fundamental  property  of  irrita- 
bility, i.e.,  it  can  be  influenced  by  external  stimuli  and  the  effect 
of  such  stimuli  can  be  transmitted  to  parts  at  a  distance  from  the 
point  of  application.  In  animals  one  kind  of  tissue  has  developed 
this  property  to  a  marked  degree,  namely  nervous  tissues.  Con- 
duction of  the  impulse  aroused  by  stimulating  a  nerve  is  so  rapid 
that  through  the  mediation  of  the  nervous  system,  integration  of 

the  organism  is  brought 
about.  The  animal  acts  as 
a  unit  not  as  a  composite 
of  unrelated  parts.  Nerve 
fibres  are  similar  to  the 
~^  wires  of  a  telegraph  system 

which  connect  the  different 
parts    of    a    country    with 

FIG.  13.     Dissection  of  the  frog's  gracilis  muscle  ,        tu  pllt  tup  wl'rPc 

to  demonstrate  that  a  nerve  conducts  in  both  direc-          eacn   Otner.      ^UL         ^  WIT 
tions.     Stimulation  at  (a)  will  cause  contraction  of  j  i 

both(a)and(&)orru*wrjo.  and     communication      be- 

tween parts  is  lost.      Cut 

the  nerves  to  an  organ  and  it  loses  its  coordination  with  the  rest 
of  the  body. 

Just  as  in  a  wire  so  in  a  nerve  fibre,  conduction  can  take  place 
in  both  directions.  This  can  be  shown  by  means  of  a  galvano- 
meter. Stimulation  of  a  fibre  in  the  middle  of  its  course  will 
cause  a  deflection  of  a  galvanometer  no  matter  at  which  end  it  is 
placed.  The  following  experiment  also  proves  the  truth  of  the 
statement. 

Experiment  18.— Kuehne's  gracilis  experiment. — Expose  the 
inner  surface  of  a  gracilis  muscle  in  a  frog.  It  will  be  seen  that 
the  two  portions  of  the  muscle  are  fed  by  branches  of  the  same 
nerve.  Separate  the  two  parts  of  the  muscle  without  injury 
to  the  nerves.  It  is  possible  to  do  this  so  that  the  nerve  is  the 
only  connection  between  the  two  parts  (Fig.  13). 

46 


NERVE  47 

Stimulation  of  either  branch  of  the  nerve  will  cause  con- 
traction of  both  muscle  masses.  In  one  case  the  impulse  must 
travel  to  the  right  at  the  junction  of  the  two  nerves  and  in  the 
other  to  the  left.  Therefore  an  impulse  can  pass  in  either 
direction  in  a  nerve. 

Nerve  fibres  are  classified  into  two  groups,  depending  upon  the 
direction  in  which  the  impulses  usually  travel.  Those  which  carry 
toward  the  brain  and  cord  are  called  afferent,  while  those  carrying 
impulses  in  the  opposite  direction  are  designated  as  efferent.  The 
latter  activate  muscles  and  glands.  Each  type  of  fibre  can  conduct 
in  both  directions,  but  in  their  normal  location,  conditions  are  so 
arranged  that  impulses  generally  start  only  at  one  end — in 
afferent  nerves  at  the  peripheral  end,  in  efferent  nerves  at  the 
central  end.  Even  though  an  efferent  nerve  be  stimulated 
at  its  peripheral  end,  the  impulse  travels  only  as  far  as  the  synapse 
or  connection  with  the  next  nerve  cell  or  neurone.  In  other  words 
the  synapse  allows  the  passage  of  impulses  in  one  direction  only— 
in  sensory  nerves,  inward,  i.e.,  towards  the  central  nervous  system; 
in  motor  nerves,  outward;  i.e.,  towards  the  periphery. 

When  we  consider  the  necessity  of  careful  insulation  to  prevent 
the  spreading  of  an  electric  current  in  contiguous  wires,  it  is  ex- 
tremely interesting  to  know  that  there  is  complete  isolation  of 
impulses  travelling  along  contiguous  nerve  fibres.  If  this  were  not 
the  case,  endless  confusion  would  result  where  great  numbers  of 
both  afferent  and  efferent  fibres  are  closely  bound  up  in  the  same 
nerve  trunk. 

Experiment  19. — The  object  of  this  experiment  is  to  determine 
whether  nerve  impulses  travelling  over  certain  fibres  in  a  nerve 
trunk  spread  to  all  the  fibres  in  that  trunk  or  remian  insulated 
in  fibres  with  which  they  are  travelling  on  entering  the  trunk. 
Pith  a  frog,  remove  the  viscera  and  the  skin  of  the  legs.  Lay 
it  on  its  back  on  a  glass  plate.  The  various  nerves  which  make 
up  the  sacral  plexus  may  each  be  stimulated  by  unipolar  induc- 
tion. To  do  this  connect  the  tissues  of  the  back,  by  means  of  the 
plate  electrode  and  a  wire,  to  the  gas  or  water  pipes  leading  to 
the  ground. 

A.  Attach  to  another  wire  a  pithing  needle  and  fasten  the 
wire  to  one  post  of  the  secondary  coil  of  the  inductorium.  With 


48  EXPERIMENTAL  PHYSIOLOGY. 

the  inductorium  arranged  for  minimal  tetanizing  currents  touch 
the  various  sacral  nerves  with  the  needle  and  observe  whether 
the  same  or  different  muscles  respond  in  the  case  of  stimulation 
of  each  nerve. 

With  the  aid  of  figure  4  make  a  table  indicating  which 
muscles  are  supplied  by  each  nerve. 

B.  Cut  the  trunk  of  the  sciatic  nerve  high  in  the  thigh  and 
repeat  the  observations. 

What  answer  does  this  experiment  give  to  the  question 
raised  in  the  1st  Paragraph? 

Why  is  it  necessary  to  do  experiment  B.  before  this  answer 
can  be  given? 

How  can  you  explain  excitation  by  the  method  of  unipolar 
induction? 

Summation  of  Inadequate  Stimuli. 

An  impulse  passing  along  a  nerve  produces  a  change  in  the 
nerve  whether  it  is  sufficient  to  cause  a  visible  response  in  its 
muscle  or  not.  The  nerve  is  left  for  a  very  brief  period  in  a  more 
sensitive  condition  so  that  a  stimulus  which  is  insufficient  when 
applied  once,  may  bring  the  end-organ  into  action  if  applied  several 
times  in  close  succession. 

Experiment  20. — Choose  a  stimulus  which  is  just  below  the 
threshold  of  that  necessary  to  cause  contraction  of  a  muscle 
through  its  nerve.  Now  apply  a  rapid  series  of  these  stimuli. 

Velocity  of  the  Nervous  Impulse. 

The  time  required  for  the  passage  of  an  impulse  along  a  nerve 
trunk  can  be  determined  by  means  of  a  sensitive  galvanometer  or 
by  the  method  described  in  the  experiment  below  where  the  response 
of  a  muscle  is  used. 

Helmholtz,  by  means  of  a  myogram  of  the  thenar  muscle  when 
stimulated  through  the  median  nerve  at  the  axilla  and  then  at 
the  wrist,  estimated  that  the  rate  in  man  was  30-35  meters  per 
second. 

Piper,  by  means  of  the  string-galvanometer,  has  studied  the 
same  nerve  and  found  the  rate  to  be  as  high  as  125  meters  per 
second. 


NERVE.  49 

Non-medullated  fibres  seem  to  conduct  more  slowly,  the  rate 

being  as  low  as  8  meters  per  second. 

Experiment  21. — Although  the  rate  of  transmission  of  the  nerve 
impulse  is  rapid,  it  can  be  determined  by  a  high  speed  kymo- 
graph. Prepare  a  gastrocnemius  muscle  with  the  nerve  as 
long  as  possible.  Clamp  the  femur  in  the  moist  chamber,  then 


FIG.  14.  Tracing  to  show  rate  of  conduction  of  the  nervous  impulse,  (i)  Contraction 
of  the  gastrocnemius  when  the  electrodes  are  near  the  muscle;  (2)  contraction  resulting 
from  stimulation  at  the  far  position.  Stimulation  at  X. 

lay  the  nerve  across  two  sets  of  cork-held  electrodes.  One 
pair  should  be  close  to  the  muscle  and  the  other  as  far  away  as 
possible.  Avoid  stretching  the  nerve.  The  electromagnetic 
signal  is  placed  in  line  with  the  point  of  the  muscle  lever 
and  alignment  marks  made  on  the  smoke-drum.  The  signal 
and  kymograph  are  connected  in  the  primary  circuit.  Adjust 


50  EXPERIMENTAL  PHYSIOLOGY. 

the  muscle  lever  so  that  only  the  beginning  of  the  contraction 
is  recorded. 

Using  the  base  line  each  time,  record  the  interval  of  the  latent 
period,  first  for  the  far  position  of  the  electrodes  and  then  for 
the  near  position.  This  can  be  done  by  changing  the  wires  of 
the  secondary  over  to  the  electrode  desired  in  each  case.  Esti- 
mate the  duration  of  the  latent  period  by  means  of  a  tuning 
fork  tracing  (Fig.  14). 

The  time  required  for  the  passage  of  the  impulse  along  the 
nerve  is  the  difference  between  the  latent  periods  resulting  from 
the  far  and  near  stimulations.  The  length  of  nerve  traversed 
may  be  taken  as  the  distance  between  the  nearer  points  of  the 
two  electrodes. 

Determine  the  velocity  of  the  nerve  impulse  in  meters  per 
second.  Make  four  or  more  sets  of  records.  Tabulate  the 
results.  (This  expt.  may  also  be  done  with  the  Harvard  drum 
as  in  Expt.  8.) 

FACTORS  INFLUENCING  NERVE  FUNCTION. 

Mechanical. — If  a  nerve  is  stretched  or  compressed  its  power 
to  conduct  may  be  lost.  When  the  compression  is  neither  too 
severe  nor  too  prolonged  conductivity  may  be  re-established. 
Compression  over  a  broad  area  requires  much  greater  force  to 
paralyze  than  when  over  a  narrow  region.  The  first  effect  of  com- 
pression, frequently,  is  to  increase  the  excitability.  This  stage, 
however,  is  quickly  passed. 

Thermal. — Beginning  with  0°  C.  the  rate  of  conduction  in- 
creases as  the  temperature  is  raised.  Below  0°  C.  conduction  is 
suspended.  At  the  higher  limit  of  conduction,  about  47°  C.  in 
the  mammal,  due  to  coagulation  of  the  proteins  the  nerve  may 
become  permanently  paralyzed. 

Chemical. — Many  drugs  lower  or  suspend  conductivity  when 
applied  locally.  Ether,  chloroform,  chloral,  cocaine,  phenol  and 
alcohol  have  this  power.  Conduction  will  return  in  time  if  the 
drug  does  not  act  too  long.  Lack  of  oxygen  will  also  destroy  con- 
ductivity in  time. 
*Experiment  22.— The  Action  of  Carbon  Dioxide,  Ether,  and 

Chloroform  upon  Nerve.— A  gastrocnemius  muscle  with  its 


NERVE.  51 

nerve  attached  is  fastened  to  a  lever  so  that  its  contraction  can 
be  recorded.  The  nerve  is  passed  through  the  two  openings 
in  the  bottom  of  the  gas  chamber.  These  holes  are  made  air- 
tight with  a  paste  made  of  kaolin  and  isotonic  NaCl  solution. 
One  pair  of  electrodes  is  set  so  that  the  nerve  within  the  chamber 
can  be  stimulated,  another  touches  the  nerve  at  the  end  farthest 
from  the  muscle.  Minimal  break  shocks  are  to  be  used  for 
stimulation.  Carbon  dioxide  is  passed  through  the  chamber, 
stimuli  being  applied  from  time  to  time  at  both  electrodes  in 
order  to  discover  changes  in  the  response. 

Wash  out  the  carbon  dioxide  by  passing  air  through  the 
chamber.  When  the  nerve  is  again  normal  blow  ether  vapour 
through  until  it  affects  the  nerve,  or  if  necessary  paint  the 
nerve  with  ether.  Do  not  prolong  anaesthesia  too  long  or  it 
will  be  difficult  for  the  nerve  to  recover.  In  a  like  manner 
study  the  influence  of  chloroform. 

Electrical. — When  a  direct  current  is  passed  through  a  nerve 
the  excitability  around  the  kathode  is  increased,  while  around  the 
anode  it  is  decreased.     The  changed  condition  produced  by  the 
direct  current  is  called  electrotonus — katelectrotonus  in  the  first 
case  and  anelectrotonus  in  the  second  case.     Midway  between  the 
two  electrodes  there  is  a  point  where  the  excitability  of  the  nerve 
has  not  been  changed.     This  indifferent  point  moves  toward  the 
kathode  as  the  current  is  increased  and  in  the  opposite  direction 
as  the  current  is  decreased.     This  can  be  shown  by  stimulating 
the  nerve  along  its  course  during  the  passing  of  the  direct  current. 
Experiment    23. — Electrotonus    in    Nerve. — When    a'  direct 
current  is  to  be  passed  through  a  tissue  for  any  length  of  time 
non-polarizable  electrodes  must  be  used  as  the  ordinary  elec- 
trodes are  easily  polarized,  thus  altering  the  efficiency  of  the 
current.      The    former    consists    of    two    boot-shaped    porous 
receptacles  which  are  partly  filled  with  a  10%  ZnSO4  solution. 
A  piece  of  pure  zinc  attached  to  the  source  of  current  is  inserted 
into  each  boot.     The  boot  is  kept  moist  on   the  outside  by 
isotonic  NaCl  solution,  the  porous  material  acting  as  a  barrier 
to  the  passage  of  zinc  sulphate  during  the  time  usually  con- 
sumed in  an  experiment. 

The  boots  must  be  kept  clean.     Each  time  after  using  they 


52 


EXPERIMENTAL  PHYSIOLOGY. 


should  be  thoroughly  washed  with  water  and  then  soaked  in 
isotonic  NaCl  solution.  When  in  use  the  ZnSO4  must  not  be 
allowed  to  spill  over  as  it  is  injurious  to  the  nerve. 


The  boots  are  held  in  position  by  the  clips  on  the  horizontal 
rod  of  the  moist  chamber  base  (Figs.  15  and  16). 

A  gastrocnemius  muscle,  with  a  long  fresh  nerve  attached,  is 


NERVE. 


53 


arranged  in  a  moist  chamber  with  the  nerve  lying  on  a  pair  oi 
electrodes  in  cork  near  the  muscle  and  a  pair  of  boot  electrodes 
farther  out.  Adjust  the  induction  coil  so  that  a  break  shock 
just  causes  contraction  of  the  muscle  through  the  electrodes 
in  cork.  Record  the  height  of  this  contraction  either  on  a 
slow  or  stationary  drum.  Next  connect  the  boot  electrodes 


FIG.  16.  Top  view  of  moist  chamber  in  the  preceding  figure,  showing  the 
arrangement  of  the  electrodes  (c)  from  the  secondary  coil  in  relation  to  the  boot 
electrodes.  Nerve  (h)  is  shown  across  the  two  sets  of  electrodes.  (6)  connects  with 
secondary,  (a)  connects  with  direct  current  supply. 


to  the  current  from  the  rheostat  so  that  the  kathode  is  nearer 
the  muscle.  Try  two  volts  at  first.  Determine  which  boot  is 
kathode  and  which  is  anode  by  dipping  the  two  wires  into 
NaCl  solution ;  bubbles  of  hydrogen  will  issue  from  the  kathode. 
While  the  constant  current  is  flowing  through  the  nerve  by 
way  of  the  boot  electrodes,  stimulate  the  nerve  with  the  same 


54  EXPERIMENTAL  PHYSIOLOGY. 

break  induced  shock  as  before.  Then  change  the  wires  to  the 
boots  so  that  the  anode  is  nearer  the  muscle,  and  stimulate  with 
the  same  break  induction  shock. 

Increase  the  direct  current  and  test  the  condition  at  the 
kathode  and  anode  as  before.  A  certain  strength  of  current  is 
necessary  to  produce  marked  changes  in  the  region  of  the 
kathode  and  anode.  It  is  possible  to  ^ompletelyj^pTock  the 
passage  of  impulses  by  means  of  a  direct  current  in  the  anodal 
region.  The  reverse  effect  is  obtained  in  the  kathodal  region. 

These  electrotonic  changes  in  the  nerve  only  last  for  a  short 
time  after  which  the  reverse  effect  may  occur.  By  reversal  it  is 
meant  that,  e.g.,  around  the  kathode  the  stage  of  increased 
excitability  finally  gives  way  to  a  condition  of  lowered  excita- 
bility. This  reversal  developes  more  quickly  with  a  strong 
current. 

STIMULATION    BY    CONTINUOUS    DIRECT    CURRENT. 

A  direct  electric  current  will  produce  stimulation  of  a  nerve 
or  muscle  when  there  is  a  quick  change  in  intensity.  This  occurs 
at  the  make  or  break,  but  apparently  not  during  the  passage  of 
the  current.  That  there  is  an  effect  during  the  passage  of  the 
current  is  shown  in  the  following  experiment. 

Experiment  24. — Cut  the  skin  on  the  ventral  surface  of  a  pithed 
frog  so  that  the  sheet  of  abdominal  muscles  is  disclosed.  The 
rectus  abdominis  is  divided  into  right  and  left  halves  by  a 
longitudinal  band  of  connective  tissue,  the  linea  alba.  Each 
half  is  further  subdivided  into  bellies  by  five  transverse  tendi- 
nous intersections.  Place  one  electrode  at  the  anterior  end 
of  either  the  right  or  left  abdominis,  and  the  other  at  the 
posterior  end,  having  a  reversing  key  in  the  circuit.  It  will 
be  found  that  at  the  kathode  of  each  belly,  i.e.,  where  the 
current  leaves  the  muscle,  there  is  a  slight  ridge  due  to  con- 
traction of  the  muscle  as  long  as  the  current  is  passing.  If  the 
direction  of  the  current  is  reversed  the  contraction  again  occurs 
at  the  kathode. 

It  can  be  shown  that  the  stimulus  caused  by  making  a  direct 
current  arises  at  the  kathode,  while  that  caused  at  the  break 
arises  at  the  anode.  If  the  kathode  and  anode  are  placed  far  apart 


NERVE.  55 

on  a  motor  nerve  the  latent  period  for  contraction  of  the  muscle 
is  greater  at  make  when  the  kathode  is  in  the  far  position,  than 
when  it  is  in  the  near  position.  Likewise  at  the  break  the  latent 
period  is  greater  when  the  anode  is  in  the  far  position  than  when 
in  the  near  position.  Therefore  the  galvanic  make  stimulus  is 
kathodal  and  the  break  stimulus  anodal. 

Electrotonus,  Kathodal  and  Anodal  Contractions  in  the 

Heart. — Because  of  the  regularly  occurring  contractions  the  heart 

is  an  admirable  muscle  for  the  study  of  electrotonic  changes  as 

well  as  the  effect  of  kathodal  and  anodal  stimulation. 

*Experiment  25. — Destroy  the  brain  of  a  frog  and  expose  the  heart 

with  as  little  hemorrhage  as  possible.    Two  boot  electrodes  are 

prepared  by  attaching  a  tiny  strip  of  cotton  wool  to  each  at 

the  toe.     The  cotton  is  soaked  with  isotonic  NaCl  solution 

and  serves  as  a  contact.      The  kathode  is  made  to  touch  the 

frog's  mouth  while  the  anode  touches  the  ventricle.    Now  if  the 

current  is  closed  during  contraction  of  the  ventricle,  it  will  be 

seen  that  at  the  moment  of  closing  the  latter  fails  to  contract 

in  the  region  of  the  anode.    This  is  due  to  the  anelectrotonus 

set  up  around  the  anode.    Of  course  only  a  limited  area  will  be 

affected,  so  that  very  close  observation  will  be  necessary.* 

Now  if  the  current  is  broken  during  diastole  the  ventricle 
will  contract  slightly  in  the  neighbourhood  of  the  anode. 
This  is  the  anodal  opening  contraction. 

The  condition  produced  in  muscle  by  the  kathode  can  be 
studied  by  changing  the  electrodes  so  that  the  kathode  touches 
the  ventricle  and  the  anode  the  mouth.  At  the  closing  of  the 
circuit  the  ventricle  contracts  in  the  region  of  the  kathode,  if 
it  is  in  diastole.  This  is  called  the  kathodal  closing  contrac- 
tion. If  the  current  is  passing  during  systole  there  may  be  a 
small  area  of  heightened  contraction  around  the  kathode. 
This  is  due  to  the  katelectrotonus. 

The  response  at  make  and  break  depends  upon  the  strength 
of  current  and  upon  whether  the  kathode  or  the  anode  is  next  to 
the  muscle. 

With  the  KATHODE  NEAR  THE  MUSCLE  a  contraction  is  obtained 

*The  local  contraction  or  failure  of  contraction  is  revealed  by  a  change  in 
color  due  to  variations  in  the  blood  content  of  the  heart  tissue  as  the  affected  part. 


56  EXPERIMENTAL  PHYSIOLOGY. 

at  the  make  whether  the  current  be  weak,  medium  or  strong. 
But  with  this  position  of  the  kathode,  contraction  is  obtained  at 
the  break  when  only  a  medium  current  is  used.  The  break  stimulus 
always  being  less  effective  than  the  make,  its  effect,  when  a  very 
weak  current  is  used,  will  be  below  the  threshold  of  stimulation. 
On  the  other  hand  when  very  strong  currents  are  used,  the  break 
stimulus  being  anodal,  is  blocked  in  the  nerve  by  the  development 
of  electrotonic  changes,  so  that  the  impulse  does  not  reach  the 
muscle. 

When  the  ANODE  is  NEAR  THE  MUSCLE,  a  weak  current  causes  a 
contraction  at  the  make,  but  has  no  effect  at  break,  not  having 
reached  the  threshold.  With  medium  currents  both  make  and 
break  are  effective.  In  the  case  of  strong  currents,  the  break  is 
effective  because  it  occurs  at  the  anode,  which  is  near  the  muscle 
with  nothing  to  block  it.  The  make  occurring  at  the  kathode 
has  to  traverse  the  whole  region  of  the  anode  at  the  time  when 
the  anode  produces  its  greatest  block  to  conduction,  i.e.,  immedi- 
ately after  making  the  current. 

We  do  not  know  the  nature  of  the  nerve  impulse,  but  whatever 
it  is,  an  electrical  change  always  accompanies  it.  This  can  be 
shown  by  connecting  a  sensitive  galvanometer  to  the  nerve.  For 
the  same  reasons  as  in  the  muscle,  the  galvanometer  will  show  a 
DIPHASIC  VARIATION,  that  is  a  deflection,  first  in  one  direction  and 
then  in  the  opposite  direction. 

METABOLISM  IN  NERVE. 

The  metabolism  in  nerve  is  so  slight  that  it  is  very  difficult  to 
obtain  indications  that  such  changes  are  going  on. 

So  far  it  has  been  impossible  to  demonstrate  the  production 
of  heat  in  nerve.  Hill  has  used  a  thermo-electric  couple  sensitive 

to  ioo^boiooo  °c  without  a  posit!ve  result' 

Every  living  cell  respires,  i.e.,  it  is  constantly  producing  CO2  but 
cells  manifesting  increased  activity  such  as  a  contracting  muscle 
show  an  increase  in  CO2  production.  Tashiro  claims  that  the 
quantity  of  CO2  produced  by  a  nerve  in  action  is  more  than  double 
that  produced  by  a  resting  nerve.  If  this  is  correct  it  indicates 
metabolic  changes  during  the  passage  of  the  nervous  impulse. 


NERVE.  57 

The  necessity  for  oxygen  is  a  further  indication  of  increased  meta- 
bolism during  activity.  Nevertheless,  nerve  must  use  an  infini- 
tesimal amount  of  energy  in  its  work,  not  only  in  view  of  the  above 
considerations,  but  because  it  is  very  difficult  to  fatigue. 

A  nerve  has  been  stimulated  continuously  for  ten  hours  and 

still  transmitted  impulses,  as  could  be  shown  by  a  galvanometer 

or  by  preventing  the  fatigue  of  the  muscle  which  is  done  by  blocking 

the  contraction  with  curare,  cold  or  a  narcotic.     Then  at  the  end 

of  the  time,  the  block  being  removed,  the  muscle  contracted. 

Experiment  26.— The   Resistance   of   Nerve   to   Fatigue.— 

Arrange  two  nerve  muscle  preparations  so  that  they  support 

levers  in  such  a  position  that  they  can  write  one  above  the 

other  upon  the  same  drum.    Both  nerves  are  to  lie  side  by  side 

on  the  same  pair  of  electrodes.     Abolish  the  conductivity  of 

one  nerve  by  keeping  it  moistened  with  ether.    Keep  the  nerve 

moist    by    improvising    a    moist    chamber    from    filter    paper. 

Stimulate  the  nerves  by  means  of  a  tetanizing  current  and 

obtain  a  record  of  the  contraction  upon  a  slowly  moving  drum. 

If  sufficient  ether  is  used  the  muscle  on  that  side  should  not 

contract.      As   soon   as   this   stage   is   reached,    tetanize   both 

nerves  until  the  active  muscle  is  exhausted.     When  this  stage 

is  reached,  wash  away  the  ether,  with  iso tonic  NaCl  solution, 

continuing  the  stimulation.    The  muscle  upon  the  treated  side 

should  soon  begin  to  contract. 

It  can  be  shown  further  that  the  fatigued  muscle  will 
respond  by  direct  stimulation.  Therefore  if  nerve  fibres  are 
still  carrying  impulses  as  is  shown  by  response  of  the  other 
muscle,  the  seat  of  fatigue  must  be  between  nerve  fibre  and 
muscle  fibre,  or  at  the  end  plate.  The  end  plate  according  to  this 
becomes  fatigued  much  earlier  than  the  muscle  fibre  and  thus 
saves  the  fibre  from  excessive  fatigue. 

THE  ALL-OR-NONE  PRINCIPLE  IN  NERVE  AND  MUSCLE. 

Stimulation  of  a  muscle  either  directly  or  through  its  nerve  pro- 
duces a  step-like  increase  in  response,  when  successively  increasing 
stimuli  are  used.  When  once  a  step  has  been  established  further 
increase  of  the  stimulus  causes  no  increase  of  contraction  until  a 
new  step  is  reached.  The  maximum  contraction  of  the  whole 


58  EXPERIMENTAL  PHYSIOLOGY. 

muscle  is  frequently  reached  in  a  few  definite  steps.  The  number 
of  steps  is  never  greater  than  the  number  of  motor  nerve  fibres  sup- 
plying the  muscle.  The  cutaneous  dorsi  nerve  of  the  frog  contains 
only  eight  nerve  fibres  and  each  nerve  fibre  supplies  a  large  num- 
ber of  muscle  fibres,  150  to  200.  Lucas  found  that  upon  gradually 
increasing  a  stimulus  to  this  nerve  from  sub-minimal  to  supra- 
maximal  that  there  were  never  more  than  eight  steps  in  the  height 
of  muscular  contraction. 

Experiment  27.— Adrian's  Experiment.— The  object  of  this 
experiment  is  to  determine  whether  a  nerve  impulse  which  is 
reduced  in  strength  by  passing  through  an  area  of  narcosis  can 
regain  its  strength  on  entering  a  normal  part  of  the  nerve  fibre. 
A  large  frog  should  be  selected  and  from  it  two  nerve  muscle 
preparations  made,  taking  care  not  to  injure  the  nerves  and  to 
procure  their  entire  length  from  their  origin  in  the  cord. 

It  is  unnecessary  to  arrange  recording  apparatus  for  this 
experiment.  The  narcotizing  chamber,  Fig.  16a,  should  be 
carefully  dried  and  placed  on  a  dry  glass  plate.  The  glass  dome 
of  the  moist  chamber  should  be  lined  with  moist  filter  paper 
so  that  it  may  be  used  to  cover  the  preparation  during  the 
experiment.  Arrange  inductorium  so  that  single  induced  shocks 
may  be  obtained  from  the  electrodes.  The  nerves  are  to  be 
laid  along  the  grooves  of  the  narcotizing  chamber,  their  proximal 
ends  being  in  vaseline  at  the  points  where  the  grooves  open  into 
the  circular  cups,  and  care  taken  that  the  grooves  are  dry  so 
that  when  the  narcotic  is  introduced  into  the  cups  it  will  not 
flow  back  along  the  grooves. 

When  this  is  done  regulate  the  strength  of  the  stimulus  so 
that  the  muscles  respond  maximally  to  break  shocks,  but  do  not 
respond  to  make  shocks.  Now  introduce  enough  15%  alcohol 
made  up  in  Ringer's  fluid  into  the  cups  of  the  moist  chamber. 
At  20  second  interval  stimultae  the  preparations,  watching  to 
see  if  either  of  them  fail,  to  contract.  Determine  how  long  each 
one  continues  to  respond. 

When  the  first  preparation  fails  to  respond  to  a  single  shock 
try  sending  in  a  series  of  shocks  in  as  rapid  succession  as  possible. 
If  a  response  occurs  it  is  due  to  summation  in  conduction. 
How  is  it  explained? 


NERVE 


59 


How  do  you  know  it  is  not  a  summation  in  excitation? 

At  the  end  of  the  experiment,  if  time  permits,  the  prepara- 
tions may  be  replaced  in  salt  solution  and  the  conductivity  of 
the  nerves  restored. 


FIG.   16A. 


The  experiment  may  then  be  repeated,  exchanging  the 
position  of  the  two  preparations  so  as  to  be  sure  that  the  result 
is  not  due  to  inequalities  in  them. 


60  EXPERIMENTAL  PHYSIOLOGY. 

Measure  the  diameter  of  the  cups. 

(a)  Is  the  total  length  of  narcotic  through  which  the  impulse 
passed  greater  in  the  case  of  the  two  small  cups  or  of  the  one 
large  cup? 

(&)  Which  preparation  ceased  to  respond  first? 

(c)  Does  the  result  indicate  that  the  impulse  is  extinguished 
immediately  in  a  narcotized  region  or  by  progressive  decrement? 

(d)  How  do  you  reconcile  decrement  with  the  all  or  none 
nature  of  conduction? 

(e)  How  does  the  intervening  normal  area  between  the  two 
short  regions  of  narcosis  affect  the  strength  of  the  nerve  impulse? 

(/)  Does  the  energy  of  the  impulse  arise  from  the  stimulus 
or  from  the  nerve  fibre? 

(g)  How  does  this  experiment  prove  the  all  or  none  nature 
of  the  nerve  impulse? 

The  passage  from  one  step  to  another  took  place  without 
any  contractions  of  intermediate  size.  Muscle  fibres  therefore 
contract  either  not  at  all  or  to  an  extent  which  is  nearly  maxi- 
mal. This  is  the  all-or-none  principle.  According  to  this 
principle  when  a  muscle  mass  is  giving  a  minimal  or  sub-maximal 
•contraction  only  a  certain  number  of  fibres  is  being  called  into 
action,  the  rest  remaining  inactive. 


SECTION    IIA. 
CHAPTER   V. 

CARDIAC  MUSCLE. 

Cardiac  muscle  resembles  voluntary  muscle  in  its  cross  stria- 
tion.  The  individual  cells,  however,  are  joined  end  to  end  and 
many  of  them  interconnected  by  fork-like  projections.  Anasto- 
mosis is  so  complete  that  there  is  continuity  throughout  the  myo- 
cardium of  both  auricles  and  ventricles.  Even  in  mammals  there 
is  evidence  of  a  complete  syncytium  in  the  form  of  muscle-fibrils 
passing  from  cell  to  cell.  The  connection  between  the  auricles  and 
ventricles  consists  of  a  narrow  bundle  of  somewhat  modified 
muscular  tissue,  the  bundle  of  Kent. 

Cardiac  muscle  contracts  much  more  rapidly  than  smooth 
muscle,  but  more  slowly  than  voluntary  muscle. 

The  heart  is  involuntary  in  action,  and  undergoes  rhythmic 
contraction  throughout  life.  This  rhythmicity  is  so  well  estab- 
lished that  it  is  impossible  to  tetanize  a  herat  by  artificial  stimula- 
tion. Herein  lies  the  most  essential  difference  between  cardiac 
and  skeletal  muscles.  If  a  stimulus  is  sent  into  the  heart  during 
systole  there  is  no  result,  but  when  stimulated  during  diastole 
an  extra  contraction  follows.  The  whole  period  of  systole  is 
refractory  to  stimulation.  In  case  an  extra  contraction  is  induced 
during  diastole,  the  relaxation  which  follows  is  prolonged  to  com- 
pensate for  the  pause  which  was  missed. 

All-or-none  Principle. — The  all-or-none  principle  applies 
to  cardiac  muscle  as  well  as  to  voluntary  muscle,  in  fact  it  was 
first  observed  in  the  former.  Due  perhaps  to  the  syncytium-like 
structure  of  the  heart  muscle,  all  of  its  fibres  have  the  same  threshold 
of  stimulation,  so  if  one  contracts  all  contract.  Moreover  as  in 
voluntary  muscle,  those  fibres  which  contract,  do  so  to  their  full 
extent  if  at  all.  Therefore  the  whole  heart  contracts  to  the  maxi- 
mum or  not  at  all. 

61 


62  EXPERIMENTAL  PHYSIOLOGY 

Action  of  Cations  on  Cardiac  Muscle.— The  ions  found 
in  the  blood  play  a  very  important  role  in  the  maintenance  of  the 
normal  heart  beat.  Remove  one  of  these  essential  ions  and  the 
heart  finally  stops  beating. 

The  SODIUM  IONS  not  only  play  a  large  part  in  the  maintenance 
of  the  normal  osmotic  pressure  but  when  present  alone,  they  pro- 
duce relaxation  of  the  heart. 

POTASSIUM  IONS  are  present  in  much  smaller  quantity  than 
sodium  and  are  not  so  essential.  They  tend  to  produce  relaxation 
and  when  increased  above  normal  the  heart  rate  is  reduced,  then 
finally  the  heart  stops  in  extreme  diastole. 

CALCIUM  IONS  are  absolutely  essential.  Excess  of  calcium 
produces  calcium  rigor,  that  is  the  heart  finally  stops  in  systole. 
Calcium  is  supposed  to  promote  contraction,  while  sodium  and 
potassium  aid  in  relaxation. 

Temperature  Effects. — Although  the  mammalian  heart  is  so 
protected  in  an  organism  with  a  relatively  constant  temperature, 
it  is  influenced  by  thermal  changes  if  subjected  to  them.  In  fact 
it  acts  like  the  heart  of  a  frog  or  turtle,  except  that  it  does  not 
withstand  the  effects  of  a  lowered  temperature  long.  The  rate 
increases  with  increase  of  temperature  up  to  a  certain  point. 
Below  17°  C.  the  mammalian  heart  does  not  beat,  likewise  above 
44°  C.  contraction  soon  ceases.  The  heart  of  cold-blooded  animals 
responds  at  lower  temperatures. 

NERVOUS  CONTROL  OF  THE  HEART  BEAT. 

Inhibition. — It  can  be  shown  by  stimulation  that  the  vagus 
inhibits  the  activity  of  the  heart.  Weak  stimuli  may  merely 
decrease  the  magnitude  of  the  beat.  Stronger  stimuli  slow  or  even 
stop  the  contractions.  Even  with  stimulation  intense  enough  to 
stop  the  heart,  after  a  time  the  beats  begin  to  break  through  or 
escape.  In  the  frog,  because  the  vagus  and  sympathetic  fibres  run 
together  in  the  same  trunk,  both  are  stimulated.  The  stimulus 
must  be  chosen  so  that  the  vagus  is  affected  more  than  the  accele- 
rator or  else  there  will  be  either  no  change  or  an  increase  in  rate. 
This  is  done  by  gradually  increasing  the  stimulation  until  vagal 
effects  predominate. 


CARDIAC  MUSCLE.  63 

Normally  in  the  frog  the  vagus  carries  very  few  impulses  to 
the  heart,  therefore  cutting  the  vagi  has  little  influence  upon  the 
rate.  But  in  mammals  the  vagi  continually  hold  the  heart  in 
check  so  that  cutting  of  these  nerves  permits  an  increase  in  rate. 
The  vagus  is  reflexly  called  into  action  by  sensory  stimulation. 
A  good  example  of  this  is  obtained  by  sharply  striking  the  abdomen 
of  a  frog  with  a  blunt  instrument.  Frequently  the  heart  may  be 
stopped  or  slowed  in  this  way. 

An  increased  blood  pressure  will  also  reflexly  act  along  the  vagus 
to  slow  the  heart.  This  is  due  to  the  stimulation  of  afferent  fibres 
ending  in  the  arch  of  the  aorta.  High  pressures  may  also  directly 
stimulate  the  vagus  centre. 

The  vagus  seems  to  exercise  a  beneficial  influence  on  the  heart, 
tending  to  oppose  acceleration  and  overwork  of  the  heart.  The 
vagus  is  most  effective  in  animals  which  are  accustomed  to  strenuous 
muscular  exercise  and  therefore  great  activity  of  the  heart. 

Acceleration. — Certain  fibres,  which  are  called  accelerator 
fibres,  oppose  the  action  of  the  vagus.  They  are  found  in  the 
cervical  sympathetic  beloAV  the  inferior  cervical  ganglion.  Stimu- 
lation of  these  fibres  increases  the  rate  of  the  heart  and  sometimes 
the  amplitude  as  well.  On  the  other  hand  cutting  of  these  fibres 
permits  the  vagus  to  have  full  sway  (in  the  mammal)  and  thus 
the  heart  beat  becomes  slower.  The  accelerators  are  called  into 
action  reflexly,  although  it  is  difficult  to  say  just  what  stimuli  will 
affect  the  accelerators  and  what  will  call  the  vagi  into  action. 

The  arrangement  of  opposed  fibres,  i.e.,  accelerator  and  in- 
hibitor, renders  quick  adjustment  to  changing  requirements 
easier. 

Experiment  28. — Frog's  Heart. — Pith  a  frog,  destroying  the 
brain  only.  Expose  the  heart  by  slitting  the  upper  part  of  the 
abdomen  lengthwise.  Avoid  injury  to  the  anterior  abdominal 
vein  by  cutting  a  little  to  one  side  of  the  mid-line.  Observe 
the  beating  of  the  heart,  especially  the  rate.  Then  open  the 
pericardium  and  pass  a  thread  under  the  fraenum  and  tie. 
The  fraenum  is  a  slender  band  of  tissue  which  connects  the 
posterior  surface  of  the  heart  with  the  pericardium.  Has  this 
operation  influenced  the  rate?  By  means  of  the  thread  raise 
the  heart  and  notice  the  large  veins,  the  sinus,  the  white  cres- 


64  EXPERIMENTAL  PHYSIOLOGY. 

centic  line  at  the  sino-auricular  junction  and  the  auricles. 
What  is  the  sequence  in  the  beat?  Record  the  normal  heart 
beat  by  connecting  the  tip  of  the  ventricle  to  a  heart  lever. 

Prepare  for  dissection  of  the  vagus  by  stretching  the  neck 
tissues  over  a  large  glass  rod  inserted  into  the  oesophagus. 
On  clearing  away  the  connective  tissue  near  the  angle  of  the 
jaw  three  nerves  can  be  found  running  from  below  the  angle 
diagonally  downward  (Fig.  5).  The  upper  one  glosso-pharyn- 
geal,  soon  turns  and  passes  forward;  the  lower  one  also  passes 
forward  in  a  similar  manner.  Lying  between  these  nerves 
before  they  bend  upward  can  be  found  the  third  nerve  or  vago- 
sympathetic  lying  under  the  edge  of  a  fine  muscle  which  connects 
the  angle  of  the  jaw  with  the  hyoid  bone.  Stimulate  the  vagus 


FIG.    17.     Effect  of  vagus  stimulation  upon  the  heart  of  the  turtle.     Note  the  increased 
amplitude  following  the  inhibition. 

to  make  sure  that  the  nerve  is  effective  in  modifying  the  heart 
rate  (Fig.  17).  Use  the  tetanizing  current,  beginning  with  a 
weak  current  and  gradually  increasing  if  there  is  no  effect. 
Bear  in  mind  that  the  sympathetic  is  being  stimulated  at  the 
same  time  and  therefore  its  stimulation  may  counteract  the 
effects  of  vagus  stimulation.  That  is  the  reason  that  it  is 
necessary  to  find  a  current  which  will  affect  the  vagus  more 
than  the  sympathetic.  Obtain  a  record  of  the  contracting  heart 
before  and  after  vagal  stimulation,  using  the  suspension  method 
as  shown  in  Fig.  18.  Use  the  magnetic  signal  to  mark  the 
time  of  stimulation.  If  you  fail  to  obtain  effects  from  one 
vagus,  try  the  other. 


CARDIAC  MUSCLE. 


65 


Next  stimulate  the  white  crescentic  line  with  the  electrodes. 
Inhibition  should  be  obtained. 

Apply  a  few  drops  of  1%  nicotine  solution  to  the  heart  and 
again  try  the  effects  of  vagus  and  crescentic  stimulation,  from 
time  to  time,  recording  the  results  on  the  kymograph.  Nico- 
tone  will  paralyze  the  ganglia.  Try  Atropine.  Explain  results. 


FIG.  18.     Suspension  method  for  heart  contraction. 

Experiment  29. — Stannius  Ligature. — (a)  First  Ligature.  Ex- 
pose the  heart  of  a  pithed  frog  in  the  manner  already  described. 
Pass  a  thread  behind  the  aorta.  Lift  up  the  apex  and  tie  the 
thread  so  that  the  knot  lies  on  the  crescent,  thus  separating 
the  sinus  from  the  auricles.  If  properly  done,  the  auricles  and 
ventricles  soon  cease  to  beat;  if  not,  tie  a  second  thread  nearer 
the  auricles.  If  the  relaxed  ventricle  be  gently  pricked  it 
gives  a  single  contraction.  In  a  short  time,  however,  the 
ventricle  may  begin  to  beat  regularly  but  at  a  different  rate 


66  EXPERIMENTAL  PHYSIOLOGY. 

from  that  in  the  normal  heart.     A  further  tightening  of  the 
ligature  will  again  inhibit  the  beat.     Explain  results. 

Certain  properties  of  cardiac  muscle  can  be  studied  with 
quiescent  musc?e  which  cannot  be  studied  in  a  heart  beating 
normally. 

Refractory  Period.— Arrange  to  stimulate  ventricle  with 
weakest  tetanizing  current  that  is  effective.  Increase  the 
strength  of  the  current  and  record  contractions.  How  does 
cardiac  muscle  differ  from  skeletal  muscle  in  its  response  to 
rapidly  interrupted  shocks?  Is  there  any  change  in  the  rate 
of  response  as  the  current  is  made  stronger? 

All-or-none  Law. — Using  the  same  preparation,  make  sure 
that  the  beat  of  the  auricle  and  ventricle  is  inhibited  by  the 
first  Stannius  ligature.  Arrange  the  induction  coil  for  single 
induction  shocks.  Apply  the  electrodes  to  the  ventricle  and 
find  the  weakest  break  shock  that  will  cause  a  contraction. 
Record,  then  turn  the  drum  about  2  mm.  After  15  sec.  record 
the  contraction  in  response  to  a  slightly  increased  stimulus. 
Turn  the  drum  again  and  increase  the  stimulus  a  little  more 
and  so  on  until  the  heart  is  receiving  the  maximal  stimulus. 
Does  the  height  of  the  contraction  under  these  conditions  vary 
with  the  strength  of  the  stimulus?  Compare  with  skeletal 
muscle.  An  interval  of  15  sec.  is  used  because  a  short  interval 
would  give  the  " staircase"  effect.  How  is  this  effect  to  be 
reconciled  with  the  "all-or-none  law"? 

(b)  Second  Ligature.  Place  a  second  ligature  around  the 
heart  exactly  over  the  auriculo-ventricular  groove.  Tighten 
this  ligature  so  as  to  compress  the  heart  between  the  ventricle 
and  the  auricles.  Note  that  the  ventricle  immediately  begins 
to  beat,  while  the  auricles  continue  in  the  relaxed  condition. 
Give  a  reason  for  this  result. 

Determine  whether  it  is  possible  to  tetanize  cardiac  muscle 
by  stimulating  with  the  tetanizing  current.  Explain  your 
results. 

Experiment  30. — Study  of  the  Turtle  Heart. — A  turtle  is 
pithed  in  the  same  way  as  a  frog.  The  plastron  or  ventral 
portion  of  the  shell  is  removed  by  the  use  of  bone  forceps  and 
scalpel.  Operate  so  that  hemorrhage  is  reduced  to  a  minimum. 


CARDIAC  MUSCLE.  67 

Study  the  action  of  the  heart  and  arteries.  Examine  the 
pericardium,  then  remove  it.  Where  does  the  contraction  seem 
to  originate?  What  path  does  it  follow  in  passing  over  the 
heart?  Is  there  any  delay  in  the  passage  between  auricle  and 
ventricle? 

A-V  INTERVAL. — In  order  to  observe  the  time  relations  between 
the  contractions  of  the  auricle  and  ventricle  arrange  to  take 
simultaneous  records  of  the  two  chambers  one  directly  above 
the  other,  using  heart  levers.  Attach  the  levers  to  the  tip  of 
each  chamber  by  means  of  tiny  hooked  pins  on  the  ends  of 
threads,  but  take  care  not  to  puncture  the  wall.  By  using  a 
very  rapid  drum  the  interval  between  the  contraction  of  auricle 
and  ventricle  can  be  determined  (Fig.  19). 


FIG.  19.      Simultaneous  tracings   of  the  contraction  of  the  auricle  (a)  and 
ventricle  (v)  in  the  turtle.     Time  interval  5  sec.  (contractions  slower  than  normal). 


STIMULATION  OF  THE  VAGUS.— Dissect  out  both  vagi  high  up 
in  the  neck.  They  can  be  located  near  the  carotid  artery. 
Pass  threads  under  the  vagi  so  that  they  can  be  lifted  when 
applying  the  electrodes. 

Study  the  effect  of  stimulating  each  vagus  by  tetanizing 
currents  of  different  strengths.  Are  the  right  and  left  vagus 
nerves  equally  efficient  in  stopping  the  heart  beat?  Do  they 
both  have  exactly  the  same  effect?  Explain.  Is  there  escape 
from  inhibition?  .  Will  a  weak  current  alter  the  A-V  interval 
without  stopping  the  heart  beat?  Secure  records  to  demon- 


68  EXPERIMENTAL  PHYSIOLOGY. 

strate  the  latent  period,  the  duration  of  the  after-effect,  changes 
in  rate,  and  escapement.  (Fig.  17). 

INFLUENCE  OF  TEMPERATURE. — Continuing  with  the  same  pre- 
paration obtain  records  with  the  heart  at  the  following  tempera- 
tures: 4°,  10°,  20°,  and  30°  C.  These  temperatures  can  be 
obtained  by  pouring  Ringer's  solution  of  the  corresponding 


FIG.  20.     Refractory  period  and  compensatory  pause  in  the  heart.     Stimulation  at  X. 

temperature  over  the  heart.  How  does  temperature  influence 
the  rate  and  amplitude  of  the  beat?  What  modification  takes 
place  in  the  A-V  interval? 

EXTRA  SYSTOLE. — Remove  the  heart  by  cutting  widely  around 
the  base.  Drop  it  in  Ringer's  solution.  After  studying  it 
there  for  a  short  time,  pin  the  base  to  a  frog  board  and  attach 


CARDIAC  MUSCLE.  69 

the  apex  to  a  heart  lever.  Frequently  pour  Ringer's  solution 
over  the  preparation.  The  writing-point  of  a  magnetic  signal 
in  the  primary  circuit  is  exactly  aligned  with  the  writing  point 
of  the  heart  lever.  The  secondary  coil  is  connected  by  fine 
wires  to  the  base  and  apex  of  the  heart.  A  record  of  the  normal 
heart  is  made  upon  a  fairly  rapid  clock-work  drum.  Then 
single  break  shocks  are  sent  into  the  heart  during  different 
phases  of  the  cardiac  cycle  in  an  attempt  to  secure  an  extra 
contraction  (Fig.  20). 

During  what  phase  can  an  extra  contraction  be  produced? 
What  follows  an  extra  contraction? 

When  you  consider  that  the  heart  obtains  its  rest  only 
between  beats,  what  do  you  think  of  this  arrangement  as  a 
safeguard  against  encroachment  upon  the  rest  period? 

Next,  cut  the  ventricle  across  near  its  junction  with  the 
auricles.  If  the  ventricle  does  not  stop  beating,  cut  still  closer 
until  the  beats  disappear.  Now  pin  the  cut  surface  of  the  apex 
to  the  board  and  apply  the  wire  which  formerly  connected  the 
base  of  the  heart.  Study  the  effects  of  a  series  of  graded  single 
shocks.  How  does  this  agree  with  the  all-or-none  principle? 
Also  attempt  to  get  the  "staircase"  effect.  Try  the  effect  of 
two  successive  stimuli  in  order  to  discover  whether  there  is  a 
refractory  period. 

Experiment  31. — Perfusion  of  the  Turtle  Heart. — The  differ- 
ence of  different  inorganic  salts  upon  the  activity  of  cardiac 
muscle  can  best  be  shown  by  perfusion  experiments. 

In  order  that  the  experiment  may  have  the  greatest  chance 
of  success  you  must  understand  and  prepare  the  mechanical 
arrangements  before  beginning  the  operation.  A  small  beaker 
containing  Ringer's  solution  is  placed  on  a  shelf  or  stand  so 
that  pressure  is  obtained  for  a  siphon  connecting  the  contents 
with  a  rubber  tube  w^hich  is  long  enough  to  be  manipulated 
with  ease  when  the  time  comes  to  insert  the  cannula.  A  small 
glass  cannula  fits  into  the  lower  end  of  the  rubber  tube,  the 
flow  of  solution  being  controlled  by  a  clamp.  Make  sure  that 
the  system  of  tube  and  cannula  is  absolutely  free  from  air. 
Expose  the  heart ;  then  carefully  free  a  short  length  of  the  inferior 
vena  cava  without  puncturing  it.  Place  a  fine  ligature  around 


70  EXPERIMENTAL  PHYSIOLOGY. 

this.  Also  pass  ligatures  around  the  other  veins  which  supply  the 
sinus  venosus.  Now  with  small  forceps  pick  up  the  lower  end 
of  the  freed  portion  of  the  vena  cava.  With  small  sharp  scissors 
cut  obliquely  downward  and  forward  not  quite  halfway  through 
the  vein.  Holding  the  vein  flap  with  forceps  insert  the  cannula 
and  tie  the  ligature  securely  about  the  constriction.  Air  must 
not  be  allowed  in  the  vein  or  cannula.  Next  start  a  small  flow 
of  Ringer's  fluid,  through  the  heart,  immediately  opening  the 
aorta,  and  then  tie  off  all  the  other  veins  entering  the  sinus. 
Obtain  tracings  of  the  ventricle  by  means  of  a  heart  lever. 

Next  determine  the  effect  of  the  following  solutions  upon  the 
heart  beat.  Between  each  solution,  Ringer's  fluid  must  be 
perfused  until  the  heart  beats  normally.  When  changing  the 
siphon  from  one  beaker  to  another  keep  air  from  entering  by 
placing  the  tip  of  the  finger  over  the  opening. 

Solutions  to  be  used  are  as  follows: 

1.  0.75%  NaCl  in  distilled  water. 

2.  A  solution  containing  0.5%   NaCl  and   0.25%   KC1  in 
distilled  water. 

3.  0.75%  NaCl  in  distilled  water  to  which  a  few  drops  of  a 
5%  CaC^  solution  has  been  added. 

4.  Distilled  water. 

Experiment  31a.  Turtle  Auricle. — Suspend  the  auricles  of  a 
turtle  as  in  Fig.  8,  p.  30  of  Manual,  lining  the  beaker  with 
moistened  filter  paper.  Record  contractions  on  slow  drum. 
Does  the  heart  muscle  contract  automatically?  Does  the 
muscle  relax  to  the  same  degree  between  each  beat?  Do  these 
changes  occur  rhythmically?  Does  the  muscle  do  more  work, 
i.e.,  lift  the  weight  of  the  lever  through  a  greater  distance,  when 
contracting  after  a  greater  relaxation  or  after  a  less  relaxation? 
The  effect  of  cations  on  cardiac  muscle  is  readily  shown  by 
immersing  the  suspended  turtle's  auricle  in  the  solutions  listed 
in  the  previous  experiment. 


CHAPTER   VI. 
BLOOD  PRESSURE. 

EFFECT   OF  CHEMICAL   SUBSTANCES  ON  THE  BLOOD 
VESSELS  AND  HEART. 

The  blood  stream  must  be  maintained  at  a  certain  pressure  in 
order  to  furnish  the  tissues  a  sufficiently  rapid  supply  of  oxygen  and 
nutrition  as  well  as  to  carry  away  waste  products.  The  heart  is 
directly  responsible  for  the  movement  of  blood,  so  that  any  increase 
in  its  output  will  increase  the  movement.  Such  an  increase  may  be 
obtained  either  by  a  greater  rate  or  a  greater  amplitude. 
Both  means  are  used. 

The  blood  pressure  would  tend  to  fall  to  zero  between  the  con- 
tractions of  the  heart  if  it  were  not  for  the  elasticity  of  the  artery 
walls.  With  each  beat  of  the  heart  the  arteries  are  expanded. 
As  soon  as  the  force  of  the  heart  is  spent,  the  arteries  contract,  thus 
preventing  a  fall  to  zero.  Fluctuations  in  pressure  are  partly 
prevented  by  the  resistance  offered  by  the  capillaries. 

The  lowest  pressure  which  is  maintained  is  called  the  diastolic 
pressure,  because  it  occurs  during  the  diastole  of  the  heart.  The 
pulse  pressure  is  the  difference  between  the  systolic  and  diastolic 
pressures.  The  more  elastic  the  blood  vessels,  the  smaller  is  the 
pulse  pressure. 

The  blood  supply  to  different  regions  of  the  body  may  be  in- 
creased by  a  greater  output,  or  by  a  shifting  of  the  blood  from  one 
region  to  another.  The  latter  method  is  made  possible  by  the 
presence  of  vasomotor  nerves.  Certain  nerves  cause  constriction, 
while  others  cause  dilatation.  Thus  the  supply  to  the  muscles 
can  be  increased  by  constriction  of  the  vessels  in  the  abdominal 
organs  and  dilatation  of  those  in  the  muscles. 
Experiment  32. — The  Measurement  of  Blood  Pressure  in 

Man. — A  sleeve  containing  a  rubber  bag,  which  connects  with 

a  mercury  manometer  as  well  as  with  a  valved  rubber  bulb,  is 

71 


72 


EXPERIMENTAL  PHYSIOLOGY. 


wrapped  snugly  about  the  arm  and  fastened.  The  sleeve 
should  be  placed  high  enough  to  permit  application  of  the 
stethoscope  over  the  brachial  artery  (Fig.  21).  While  palpating 


FIG.  21.     Sleeve  in  place  for  measuring  blood  pressure.     It  should  be  high  enough  to  allow 
ample  room  for  the  stethoscope. 


BLOOD  PRESSURE.  73 

the  radial  artery  the  pressure  in  the  rubber  bag  is  raised  above 
that  necessary  to  produce  obliteration  of  the  pulse.  Now  no 
sound  can  be  heard  over  the  brachial  artery  at  the  elbow.  By 
gently  releasing  the  valve  the  pressure  is  gradually  lowered. 
Just  as  soon  as  the  pressure  becomes  less  than  systolic  pressure, 
the  blood  is  forced  through  the  occluded  arteries  and  a  distinct 
thud  is  heard  at  each  heart  beat.  At  the  same  time  or  often 
after  the  pressure  has  been  lowered  5-10  mm.  more,  the  pulse 
is  felt  at  the  wrist.  The  first  sound  is  never  below  the  tactile 
indication;  if  it  is,  some  error  has  been  made  in  the  application 
of  the  apparatus,  usually  the  stethoscope.  The  pressure  read 
at  the  time  that  the  first  sound  is  heard  is  systolic  pressure. 

As  the  armlet  pressure  is  further  lowered,  the  sound  be- 
comes progressively  louder  and  sometimes  resembles  a  murmur 
in  character,  and  then,  rather  suddenly,  it  becomes  feebler  and 
at  the  same  time  duller.  At  this  point,  the  manometer  indicates 
the  diastolic  pressure.  After  this  sudden  sound,  the  sound  may 
continue  to  be  heard  for  a  longer  or  shorter  time  as  the  armlet 
pressure  continues  to  fall. 

The  difference  between  systolic  and  diastolic  pressure  is  the 
pulse  pressure. 

Determine  the  heart  rate,  systolic  and  diastolic  pressures 
under  the  following  conditions  in  as  many  different  subjects  as 
possible: 

Supine  position,  sitting,  standing  and  immediately  after 
vigorous  exercise  as  running  up  and  down  stairs.  How  does  the 
pulse  pressure  change  under  these  conditions? 

PRINCIPLES  OF  HAEMODYNAMICS. 

The  blood  propelled  by  the  heart,  circulates  in  a  closed  system 
of  tubes.  Both  the  output  of  the  heart  and  the  response  of  the 
vessels  affect  the  rate  of  flow.  Increase  the  output  of  the  heart 
either  by  a  greater  number  of  contractions  per  unit  of  time  or  by 
increasing  the  amplitude;  either  change  will  produce  a  greater  flow 
of  blood. 

If  the  blood  circulated  in  perfectly  rigid  vessels  the  pressure  in 
the  system  would  rise  to  a  maximum  during  the  contraction  of  the 


74 


EXPERIMENTAL  PHYSIOLOGY. 


heart  and  fall  to  zero  during  the  relaxation.  The  flow  in  such  a 
case  would  be  spasmodic.  On  the  other  hand  if  the  walls  of  the 
vessels  are  elastic,  they  are  stretched  by  each  spurt  of  blood  from 
the  heart,  and  then  as  the  heart  begins  to  relax  the  distended  vessel 
wall  begins  to  contract,  thus  forcing  the  blood  onward  in  spite  of 
the  inactivity  of  the  heart.  The  elastic  wall  therefore  keeps  the 
blood  pressure  from  falling  to  zero  during  diastole. 

If  the  blood  meets  with  resistance  somewhere  in  the  path  the 
vessels  on  the  near  side  are  distended  more  than  they  would  be  if 


FIG.  22.  Circulation  scheme.  The  bulb  (a)  which  represents  the  heart  can 
have  its  output  varied  by  either  a  change  in  rate  of  compresssion  or  by  sliding  the 
block  (&)  and  thus  changing  the  amplitude.  The  openings  to  the  bulb  are  provided 
with  valves  so  that  flow  can  take  place  only  in  one  direction.  The  resistance  which 
corresponds  to  the  capillaries  is  the  part  (c),  (d).  This  maybe  varied  by  means  of 
the  clamp  (c).  The  elasticity  of  the  rubber  tubing  corresponds  to  the  elasticity 
of  the  arterial  wall.  The  "venous"  and  "arterial"  pressures  are  measured  by  mano- 
meters (e)  and  (/)  respectively. 

the  resistance  were  decreased  or  absent.  The  greater  the  distension 
of  the  tubes  the  longer  they  require  to  contract  so  that  a  steady  flow 
would  be  kept  up  for  a  longer  period.  When  the  peripheral  resist- 
ance is  constricted  venous  flow  is  regular ;  great  dilatation  produces 
an  intermittent  venous  flow. 

Experiment  33. — Circulation  Scheme. — Many  of  the  foregoing 
principles  can  be  demonstrated  by  a  simple  system  of  rubber 
tubes  (Fig.  22).  A  rubber  bulb  represents  the  heart.  The 


BLOOD  PRESSURE. 


75 


rubber  tubing  nearest  the  heart  takes  the  place  of  the  arterial 
system,  while  the  venous  system  is  the  tubing  on  the  other  side 
of  the  resistance. 

1.  With  moderate  capillary  resistance  determine  a  rate  of  bulb 
compression  which  will  cause  a  pronounced  rise  in  pressure  as 
shown  by  the  manometer.    (If  possible  both  arterial  and  venous 
manometers  should  record  in  line  vertically  with  each  other;  to 
do  this  the  arterial  pressure  zero  should  be  higher  than  that  for 
the  venous  pressure.)     By  means  of  the  block  vary  the  ampli- 
tude, but  maintain  a  constant  rate.     What  do  the  records  of 
venous  and  arterial  pressure  show?      What   can   you   say  in 
regard  to  the  venous  outflow? 

2.  With  the  same  capillary  resistance  and  with  a  moderate 
amplitude  vary  the  rate.     Obtain  pressure  records  and  note 
venous  flow. 

3.  Wi,th  the  rate  which  gives  the  best  results  and  with  moderate 
amplitude   vary   the   capillary   resistance,    recording   pressure 
changes  and  noting  venous  outflow  as  before. 


B 


z> 


// 


)       } 


FIG.  22A. 


Compare  diastolic  and  pulse  pressures  under  the  foregoing 
conditions. 

What  relation  does  capillary  resistance  bear  to  them? 

How  do  amplitude  and  rate  of  the  heart  contraction  affect 
diastolic  and  pulse  pressures? 

Experiment  33a. — The  apparatus  represented  in  Fig.  22a  may 
be  employed  to  demonstrate  the  part  which  the  peripheral 
resistance  and  the  elasticity  of  the  arterial  walls  play  in  the 


76  EXPERIMENTAL  PHYSIOLOGY. 

conversion  of  an  intermittent  flow  in  the  arteries  to  a  continuous 
flow  in  the  veins. 

The  apparatus  consists  of  a  reservoir  R,  a  pump  P,  and 
two  lengths  of  tubing,  one,  A,  of  glass  and  the  other,  B,  of 
rubber.  Each  tube  is  provided  at  its  extremity  with  a  thumb- 
screw by  which  its  calibre  can  be  varied.  A  pinch-cock,  D, 
placed  between  the  reservoir  and  the  pump,  allows  the  flow  of 
fluid  to  be  cut  off  when  the  schema  is  not  in  use. 

With  the  pinch-cock  D  closed,  fill  the  reservoir  with  water. 
Adjust  the  thumb-screws  at  the  extremities  of  the  tubes  so 
that  the  lumen  of  each  is  at  its  maximum  calibre.  Place  a 
basin  beneath  the  openings  of  the  tubes  or  direct  them  so  that 
the  fluid  issuing  therefrom  will  flow  into  the  sink.  Open  the 
pinch-cock  D.  Compress  the  bulb  intermittently  at  the  rate  of 
about  60  per  minute.  What  is  the  nature  of  the  flow  from 
tubes  A  and  B  respectively?  Next  adjust  the  thumb-screws 
so  that  the  diameter  of  each  tube  is  considerably  reduced. 
Repeat  the  intermittent  compression  of  the  bulb  closing  off 
A  or  B  by  compressing  the  rubber  tubing  next  the  Y-piece. 
What  do  you  find  with  regard  to  the  outflow  from  each  tube? 
Explain  your  results. 

Response  of  Blood  Vessels  to  Chemical  Substances. 

The  amount  of  blood  to  any  region  can  be  increased  by  an  in- 
crease in  the  output  of  the  heart  or  by  a  dilatation  of  the  blood 
vessels  in  that  region.    Dilatation  may  be  brought  about  through 
action  of  the  nerves  to  the  vessels  or  by  chemical  substances  in 
the  blood.    For  example  certain  waste  products  such  as  lactic  acid 
may  cause  dilatation.     The  blood  vessels  therefore  not  only  by 
their  elasticity  help  to  maintain  a  steady  blood  flow,  but  by  their 
active  constriction  and  dilatation  shunt  the  blood  to  regions  most 
in  need  of  it.     That  the  blood  vessels  will  respond  to  chemical 
substances,  can  be  shown  by  the  following  experiment. 
Experiment  34. — Perfusion  of  the  Frog. — Not  only  can  the 
heart  be  kept  beating  for  a  considerable  time  by  perfusion,  but 
circulation  can  be  maintained  for  some  time  through  the  blood 
vessels  as  well.      Arrange  the  beaker  and  siphon  for  perfusion 
as  used  in  the  turtle  heart.    After  exposing  the  heart  of  a  frog 


BLOOD  PRESSURE  77 

whose  brain  has  been  destroyed,  tie  off  one  aorta  and  fasten 
a  cannula  into  the  other  so  that  it  will  lead  away  from  the  heart. 
Air  must  not  be  allowed  to  enter  the  system  on  any  account. 
Hang  the  frog  toes  down  and  allow  the  fluid  to  escape  from 
an  incision  in  the  sinus  venosus.  Determine  the  rate  of  flow 
in  cc.  per  minute  for  Ringer's  solution.  This  can  be  done  either 
by  measuring  the  inflow  from  a  burette  or  by  collecting  the  out- 
flow in  a  graduated  cylinder.  Next  perfuse  with  Ringer's 
solution  containing  0.1%  NaNO2.  What  is  the  rate  now? 
Wash  out  the  latter  fluid  with  Ringer's  solution,  then  perfuse 
with  Ringer's  solution  containing  adrenalin. 

Although  adrenalin  causes  constriction  of  the  blood  vessels 
in  the  frog  and  under  certain  conditions  in  mammals,  small 
quantities  of  adrenalin  cause  dilatation  of  the  vessels  supplying 
skeletal  muscle  in  most  mammals,  when  injected  into  the  general 
circulation. 


SECTION    II  B. 
CHAPTER   VII. 

HAEMODYNAMICS 

Although  many  fundamental  facts  relating  to  the  function  of 
the  cardiovascular  system  can  be  learned  from  experiments  on 
cold-blooded  animals,  it  is  essential  for  a  proper  understanding  of 
the  physiology  of  the  circulation  in  man  that  a  certain  number  of 
experiments  be  performed  by  the  student  on  mammals.  In  order 
that  this  may  be  done  without  causing  any  pain,  the  animal  must 
be  deeply  anaesthetised  by  an  expert  assistant  before  starting  the 
experiment,  the  anaesthesia  must  be  maintained  throughout,  and 
when  the  experiment  is  finished,  the  animal  must  be  painlessly 
killed.* 

The  following  two  experiments  are  selected  to  illustrate  certain 
fundamental  factors  governing  the  circulation  of  the  blood.  Other 
fundamental  experiments  will  be  demonstrated  before  the  class. 

Each  experiment  is  performed  by  a  group  containing  from  four 
to  six  students.  Two  of  these  act  as  operators  and  are  responsible 
for  the  operative  manipulations,  one  or  two  attend  to  the  apparatus 
(technicians),  and  the  remainder  make  detailed  notes  of  every 
step  in  the  experiment.  After  the  experiment  is  completed,  the 
group  should  review  the  results  and  each  member  of  it  prepare  a 
report,  embodying  copies  of  the  tracings  secured.  These  reports 
are  to  be  handed  in  for  inspection.! 


*For  small  classes  it  is  practicable  to  have  these  essential  mammalian 
experiments  done  on  decerebrated  preparations  (see  p.  247),  but  this  is  impossible 
when  large  numbers  have  to  be  provided  for. 

fFor  the  experiments  each  student  must  provide  himself  with  the  following 
instruments:  dissecting  case,  including  1  pair  scissors  and  a  blunt  hook  (aneurism 
needle  or  strabismus  hook) ;  2  pairs,  haemostats  (Pean  or  Spencer  Wells  forceps) ; 
2  pairs,  bull  dog  forceps;  a  stethoscope. 

78 


HAEMODYNAMICS.  79 

Experiment  35. 

BLOOD  PRESSURE.  NERVE  CONTROL  OF  HEART  BEAT 
AND  PERIPHERAL  RESISTANCE.  HAEMORRHAGE 
AND  TRANSFUSION.  INSPECTION  OF  HEART. 

1.  PREPARATION  OF  ANIMAL. — Weigh  the  animal.  In  the  case  of 
dogs,  inject  morphine  solution   (sulphate  or  hydrochloride)   sub- 
cutaneously  (0.5  c.c.  of  2%  solution  per  kilo  of  body  weight).     In 
the  case  of  cats,  pass  the  stomach  tube  and  pour  the  required  amount 
of  ure thane  solution  into  the  stomach.     (Give  1  gram  of  urethane 
per  kilogram  of  body  weight,  dissolving  it  in  water  to  make  a  20% 
solution).     These  preliminary  operations  are  to  be  performed  by 
the  laboratory  technician  or  by  a  demonstrator,  with  the  students 
assisting.     In  about  one  half  hour  the  animal,  now  practically  un- 
conscious, is  completely  anaesthetised  by  administering  ether.     To 
do  this  pour  about  20  c.c.  on  a  towel  and  hold  this  firmly  over  the 
muzzle  of  the  animal,  being  careful  however  to  avoid  suffocation. 
The  animal  is  then  tied,  back  down,  on  the  animal  board,  mean- 
while deep  anaesthesia  is  maintained  by  giving  ether.     Count  the 
pulse  at  the  femoral  artery;  count  the  respirations  and  record  the 
rectal    temperature.      Note    any   peculiarities   about   the    animal 
(e.g.,  enlarged  thyroid). 

While  the  operator  and  anaesthetist  are  preparing  the  animal 
and  performing  the  necessary  operations,  the  technician  and 
other  members  of  the  group  proceed  to  get  the  manometer  tubing 
and  cannula  ready,  as  directed  in  par.  3  below. 

2.  INSERTION  OF  TRACHEAL  CANNULA.  Moisten  the  hair  in  front 
of  the  neck  and  make  a  median  incision  down  to  the  trachea  (cut 
with  the  edge,  not  with  the  point  of  the  scalpel).     Pass  a  stout 
ligature  under  the  trachea.     Make  a  transverse  incision  half  way 
across  the  trachea,  insert  the  tracheal  cannula  and  tie  it  by  means 
of  the  ligature.     The   tracheal   cannula  is  inserted   to   facilitate 
artificial  respiration  should  this  be  necessary.     If  further  anaes- 
thetic is  required,  connect  the  tracheal    cannula   with  the  wide- 
mouthed  anaesthetic  bottle  containing  some  ether. 

3.  INSERTION  OF  CAROTID  CANNULA  AND  RECORDING  OF  MEAN 
ARTERIAL  BLOOD  PRESSURE. — Pull  apart  the  skin  flaps  and  separate 
the  sterno-mastoid  and  sterno-thyroid  muscles  so  as  to  expose  the 


80 


EXPERIMENTAL  PHYSIOLOGY. 


carotid  artery.  With  an  aneurysm  needle  or  a  blunt-pointed  curved 
seeker,  free  the  carotid  from  its  sheath  for  about  an  inch  and  place 
two  ligatures  under  it.  Tie  the  peripheral  ligature  (the  one  farthest 


FIG.  23.     Stand,  manometer,  pressure  bottle,  etc.,  for  recording  blood  pressure. 

from  the  heart).     Place  a  bull-dog  forceps  on  the  artery  central 
to  the  central  ligature. 

Separate  the  vagus  nerve  from  the  carotid  sheath  on  both  sides 
of  the  neck,  and  place  ligatures,  without  tying  them,  around  both 


HAEMODYNAMICS.  81 

nerves.    Put  bull-dog  forceps  on  the  ligatures  to  prevent  these  from 
slipping  off. 

Meanwhile  a  cannula  of  suitable  size  is  connected  to  the  mano- 
meter (Fig.  23)  by  rubber  tubing  which  has  been  scrupulously 
cleaned  of  any  old  blood.  This  tubing  is  also  connected  by  a 
T-piece  with  a  bottle  provided  with  a  rubber  bulb  and  containing 
a  2%  solution  of  sodium  citrate  to  prevent  clotting  of  the  blood. 
The  cannula  must  be  scrupulously  clean  and  should  be  slightly  oiled 
before  inserting.  Observance  of  these  precautions  greatly  dim- 
inishes blood  clotting.  A  pinchcock  on  the  side  tube  which  con- 
nects with  the  bottle  is  cautiously  opened  and  by  gentle  compres- 
sion of  the  rubber  bulb,  which  is  connected  with  the  bottle,  the 
tubing  is  filled  with  the  citrate  solution  to  the  exclusion  of  all  air 
bubbles.  The  pinchcock  on  the  side  tube  is  closed  and  a  screw 
clip  is  placed  on  the  tubing  which  connects  manometer  and  cannula, 
and  closed.  The  writing  style  of  the  chronograph  is  now  adjusted 
so  that  it  corresponds  to  that  of  the  manometer.  The  line  of  the 
time  tracing  therefore  serves  as  the  line  of  zero  pressure. 

The  cannula,  filled  to  the  tip  with  the  citrate  solution,  is  now 
inserted  by  the  operator  into  the  artery  in  the  following  way:  the 
wall  of  the  artery  near  the  peripheral  ligature  is  picked  up  by  a 
forceps  and,  with  a  sharp  scissors,  a  V-shaped  cut  is  made  into  the 
artery  without  cutting  it  clear  across.  The  tip  of  the  V  points 
peripherally.  The  V-shaped  flap  is  lifted  up  with  a  fine  pair  of 
forceps  and  the  cannula  inserted  into  the  artery  and  tied  by  means 
of  the  central  ligature.  The  clip  on  the  tubing  connected  with  the 
bottle  is  opened  and  the  bulb  compressed  until  a  pressure  of  about 
120  mm.  Hg.  is  recorded  in  the  manometer.  The  pressure  in  the 
tubing  prevents  blood  from  entering  it  when  the  "bull-dog"  for- 
ceps on  the  artery  is  opened,  which  is  now  done.  The  writing 
styles  of  the  manometer  and  chronograph  are  adjusted  to  the  drum, 
and  a  tracing  is  taken  with  a  slow  speed  drum. 

4.  DEMONSTRATE  THE  EFFECT  ON  THE  BLOOD  PRESSURE  OF 
VARIATIONS  IN  THE  PUMPING  ACTION  OF  THE  HEART.  STIMULATION 
OF  PERIPHERAL  END  OF  VAGUS  NERVE. — Expose  the  vagus  nerve 
in  the  neck  on  both  sides  and  loosely  tie  the  ligatures  that  were 
previously  placed  around  each  nerve.  Start  the  drum  and  record 
a  short  piece  of  normal  tracing,  and  then,  without  stopping  the 


82  EXPERIMENTAL  PHYSIOLOGY. 

drum,  cut  first  one  and  then  the  other  vagus  between  the  ligatures. 
Note  the  effect  produced  on  the  blood  pressure  (Fig.  27).  To 
signal  the  moment  of  cutting,  short-circuit  the  time  tracing  for  a 
second  or  two.* 

Allow  several  inches  of  tracing  to  be  recorded  after  both  nerves 

have  been  cut,  so  as  to  be  able  to  determine  the  after  effects;  then 

tstop  the  drum  and  place  the  peripheral  end  of  one  vagus  on  elec- 

rode  s    coming  from  a  short  circuiting  key  which  is  meanwhile 


a  b 

FIG.  24.     Arterial  blood  pressure  tracing:  (a)  during  moderate  stimulation  of  the  peri- 
pheral end  of  vagus;  (b)  during  stimulation  of  splanchnic  nerve. 

closed.  Record  a  short  piece  of  normal  tracing  and  then  by  opening 
the  short-circuiting  key,  stimulate  the  vagus  with  an  induced  cur- 
rent that  is  just  bearable  on  the  tip  of  the  tongue  and  note  the 
effect  produced  on  the  blood  pressure.  Signal  the  time  of  stimula- 
tion as  above  directed.  Demonstrate  escapement. 

*By  short-circuiting  the  time  marker  in  this  way  the  seconds  cease  to  be 
recorded  and  the  break  in  the  otherwise  regular  time  tracing  affords  a  useful 
signal  indicating  the  moment  of  cutting  or  stimulation. 


HAEMODYNAMICS.  83 

Repeat  with  the  opposite  vagus. 

Repeat  the  experiment — using  varying  strengths  of  stimuli. 

Explain  the  results. 

5.  DEMONSTRATE  THE  EFFECT  OF  VARYING  THE  PERIPHERAL 
RESISTANCE  ON  THE  BLOOD  PRESSURE;  STIMULATION  OF  SPLANCH- 
NIC NERVE. — Make  an  incision  along  the  left  costal  margin  starting 
about  1J  inches  from  the  linea  alba.  After  stopping  all  hemorr- 
hage,* open  the  peritoneum  and  make  out  the  suprarenal  capsule 
lying  over  a  transversely  coursing  vein.  Just  outside  the  suprare- 
nal and  above  the  vein  expose  the  greater  splanchnic  nerve  by 
blunt  dissection.  Tie  a  ligature  loosely  around  the  nerve  and  lay 
this  on  electrodes.  While  recording  a  normal  tracing  of  the  blood 
pressure  stimulate  the  nerve  (Fig.  24).  In  taking  this  tracing  all 
details  are  to  be  followed  as  in  par.  4. 

Explain  the  result. 

The  splanchnic  nerve  is  difficult  to  find  unless  the  abdominal 
viscera,  with  the  exception  of  the  left  kidney,  are  well  retracted 
to  the  right.  This  is  to  be  done  by  the  assistant  operator,  who, 
standing  on  the  right  of  the  animal,  covers  the  viscera  with  cloths 
wrung  out  with  warm  0.9%  NaCl  solution,  places  the  left  hand 
with  fingers  extended  over  the  cloth,  and  then  with  the  finger  tips 
just  touching  the  posterior  wall  of  the  abdomen,  pulls  the  viscera 
towards  the  right.  With  the  right  hand  this  operator  also  pulls 
down  the  kidney  on  the  left  side.  By  these  procedures  the  suprare- 
nal capsule  is  easily  brought  into  view,  and  the  operator  isolates 
the  splanchnic  nerve  by  blunt  dissection  in  the  region  just  above 
the  capsule. 

It  is  often  simpler  to  find  the  splanchnic  nerve  on  the  right  side. 
In  this  case,  after  retraction  of  the  viscera  by  the  procedure  de- 
scribed above,  but  towards  the  left  side,  the  right  kidney  is  exposed, 
and  the  vein,  connecting  the  abdominal  muscles  with  the  adrenal  vein, 
is  ligated  in  two  places  and  cut  between  the  ligatures.  The 
splanchnic  nerve  is  then  brought  into  view  by  little  dissection. 

*The  haemorrhage  occurs  mostly  when  the  muscles  are  being  cut.  To  arrest  it 
firmly  sponge  the  wound  with  surgical  gauze,  locate  the  bleeding  points,  catch 
them  in  the  points  of  artery  forceps  (haemostats)  and  while  an  assistant  gently 
elevates  the  point  of  the  forceps,  tie  a  ligature  around  the  tissue  caught  in  them. 
For  venous  and  capillary  oozing,  pressure  with  a  piece  of  gauze  wrung  out  in  hot 
water  is  usually  sufficient. 


84  EXPERIMENTAL  PHYSIOLOGY. 

6.  DEMONSTRATE  THE  EFFECTS  OF  HAEMORRHAGE  AND  OF 
TRANSFUSION  ON  THE  MEAN  ARTERIAL  BLOOD  PRESSURE. — -Intro- 
duce a  cannula  into  the  femoral  artery  of  one  side  and  another  into 
the  femoral  vein  of  the  other  side.  The  arterial  cannula  is  intro- 
duced as  directed  above,  and  connected  with  a  piece  of  rubber  tub- 
ing through  which  to  bleed  the  animal.  The  venous  cannula  is  intro- 
duced as  follows:  The  vein  is  exposed  and  two  ligatures  placed 
underneath  it;  a  bull-dog  forceps  is  applied  central  to  the  central 
ligature,  and  the  peripheral  ligature  is  tied.  A  cannula  of  suitable 
size,  connected  with  about  six  inches  of  rubber  tubing  and  filled 


FIG.  25.  Arterial  blood  pressure  tracing  showing  the  effect  of  a  moderately  slow  hsemorrhag  -, 
followed  by  a  rapid  haemorrhage. 

with  0.9%  NaCl  solution,  held  in  by  means  of  a  clip  on  the  rubber 
tubing,  is  inserted  into  the  vein  towards  the  heart  in  exactly  the 
same  way  as  in  par.  3.  When  both  cannulae  are  in  position,  the 
tubing  on  the  venous  cannula  is  connected  with  a  burette. 

HAEMORRHAGE. — After  taking  an  inch  or  two  of  normal  tracing 
of  the  pressure  in  the  carotid  artery,  the  clip  on  the  femoral  artery 
is  partially  or  completely  removed  and  the  blood  which  escapes 
collected  in  a  basin  and  defibrinated.  Note  the  effect  on  the  blood 
pressure  (a)  of  sudden  and  (b)  of  gradual  bleeding  (Fig.  25).  It  will 
be  found  when  the  artery  is  fully  opened  that  there  is  an  immediate 
fall  in  blood  pressure  due  to  release  of  peripheral  resistance.  If  the 


HAEMODYNAMICS.  85 

clip  is  only  partially  opened,  considerable  bleeding  may  occur 
before  the  blood  pressure  is  materially  affected.  Continue  the 
bleeding  until  a  permanent  (marked)  fall  of  blood  pressure  is 
recorded.  About  25  c.c.  of  blood  per  kg.  body-weight  must  usually 
be  removed  to  obtain  this  result. 

SALINE  TRANSFUSION. — Now  connect  the  venous  cannula  with 
a  burette  filled  with  a  0.9%  NaCl  solution,  previously  warmed  to 
body  temperature;  remove  the  clip  and  allow  the  saline  to  pass 
into  the  animal,  taking  great  care  that  no  air  bubbles  are  carried 
in  with  the  solution.  Meanwhile  MAKE  OBSERVATIONS  ON  THE 
VENOUS  BLOOD  PRESSURE  (which  is  indicated  by  the  height  in  the 
burette  at  which  no  more  saline  enters  the  vein);  noting:  (a)  its 
height  in  mm.  of  water  and  (b)  whether  it  shows  any  pulsations. 
Observe  carefully  the  effect  of  the  transfusion  on  the  arterial  blood 
pressure. 

The  blood  removed  in  this  and  in  all  other  experiments  is  to 
be  defibrinated  by  beating  in  a  clean  dry  basin  with  a  bunch  of 
wires.  When  fibrin  formation  has  ceased  the  whipped  blood  is 
strained  through  muslin,  and  measured  in  a  graduated  cylinder. 

BLOOD  TRANSFUSION. — Again  bleed  from  the  femoral  artery, 
carefully  noting  the  behaviour  of  blood  pressure,  respirations,  etc. 
Note  any  differences  in  the  character  of  the  blood  from  that  ob- 
tained previous  to  the  saline  transfusion.  When  the  blood  pressure 
is  extremely  low  (40  mm.)  transfuse  with  defibrinated  blood  and 
note  the  effect  on  the  blood  pressure  as  compared  with  that  pro- 
duced by  saline  solution.  Note  particularly  with  which  solution 
the  restored  pressure  is  best  maintained. 

7.  OBSERVE  THE  HEART  BEAT  IN  THE  OPEN  THORAX  UNDER 
ARTIFICIAL  RESPIRATION. — Since  natural  respiration  is  impossible 
after  the  thoracic  cavity  has  been  opened  (explain  why)  it  is  neces- 
sary to  start  artificial  respiration  by  means  of  a  pump  connected 
with  the  tracheal  cannula.  The  air  delivered  from  the  pump  is 
in  a  continuous  stream.  In  order  to  interrupt  it  so  as  to  simulate 
the  respirations,  a  wide  T-piece  is  placed  on  the  rubber  tube 
between  the  pump  and  tracheal  cannula,  and  this  side  tube  is 
opened  and  closed  by  a  finger  at  a  rate  corresponding  to  the  normal 
respirations.  In  order  to  open  the  thorax  the  skin  is  first  of  all 
incised  down  the  mid  line  from  the  base  of  the  neck  to  well  on  to 


86  EXPERIMENTAL  PHYSIOLOGY. 

the  abdomen  and  is  quickly  dissected  to  both  sides  sufficiently  to 
expose  the  rib  cartilages.  The  latter  are  then  separately  snipped 
through  on  both  sides  by  a  bone  forceps  and  finally  the  soft  tissues 
are  cut  through  by  a  stout  scalpel  from  below  up.  Arterial  haemorr- 
hage must  be  controlled  by  catching  the  bleeding  points  with  a 
haemostat  and  tying,  but  venous  oozing  can  be  stopped  by  applying 
cloths  wrung  out  with  hot  water. 

Watch  the  heart  while  the  vagus  nerve  is  being  stimulated. 
Place  stout  ligatures  under  the  superior  and  inferior  venae  cavae 
and  tighten  them  for  a  few  moments;  note  the  emptying  of  the 
heart.  Place  a  ligature  under  the  pulmonary  artery  and  tighten 
for  a  moment.  Note  the  effect  on  the  heart.  Repeat  with  the 
aorta. 

Listen  to  the  sounds  of  the  heart  with  a  stethoscope  applied 
directly  to  various  parts  of  it  and  study  the  effect  produced  on 
the  sounds  by  tightening  the  ligatures  referred  to  above.  Stop 
the  artificial  respiration  for  a  few  moments  and  note  the  behaviour 
of  the  heart. 

Afterwards  excise  the  heart  and  open  the  right  ventricle  to 
observe  the  contractions  of  the  papillary  muscles.  Note  that  the 
first  sound  is  still  heard  in  the  excised  heart.  What  conclusion  do 
you  draw  from  this  observation? 


CHAPTER    VIII. 

Experiment  36. 

VASO  MOTOR  NERVES,  DEPRESSOR  NERVE, 
CIRCULATION  TIME. 

(The  General  Instructions  for  the  Insertion  of  the  Cannulae 

and  the  Conduct  of  the  Experiment  are  the  same  as 

in  Experiment  31). 

1.  PREPARATION  OF  ANIMAL. — Weigh  the  rabbit.     Inject  a  10% 
solution  of  chloral  hydrate  per  rectum,  5  c.c.  per  kg.  body  weight. 
When  the  chloral  effect  has  developed  (about  30  minutes)  cause  the 
rabbit  to  inhale  a  little  ether.     To  fix  the  head  make  an  incision 
through  the  floor  of  the  mouth  and  with  an  aneurysm  needle  pass 
a  stout  thread  through  the  incision  and  out  of  the  mouth.     Tie  the 
thread  to  the  cross  bar  of  the  animal  board.     Tie  out  the  limbs. 

2.  DEMONSTRATE  VASOCONSTRICTOR  FIBRES  IN  THE  CERVICAL 
SYMPATHETIC. — Clip  the  hair  from  the  front  of  the  neck  and  make 
a   median   incision.      Retract   the   skin.      Separate   the   laryngeal 
muscles  from  the  sterno-mastoid  so  as  to  expose  the  carotid  sheath. 
Running  with  the  carotid  arteries  will  be  seen  one  large  and  two 
small  nerves.     Of  the  latter,  one  is  the  cervical  sympathetic,  the 
other  the  depressor  (see  Fig.  26).      Tie  a  pair  of  ligatures  loosely 
around  each  nerve.*    Now  stretch  the  ear  on  the  same  side  as  the 
exposed  nerve  on  a  wire  frame  so  as  to  render  its  vessels   quite 
plain.    Stitch  the  edges  of  the  ear  to  the  frame.    With  a  good  light 
behind  it,  examine  the  vessels  of  the  ear,  carefully  noting    their 
size.    Note  also  the  size  of  the  pupils.    Pick  up  the  ligatures  around 
one  of  the  fine  nerves,  tie  both  ligatures  and  cut  the  nerve  between 
them.     Look  for  any  effect  on  the  vessels  of  the  ear  and  on  the 
pupils  during  both  tying  and  cutting.     Apply  electrodes  to  the 

*To  obviate  confusion  the  ligatures  should  be  marked  by  placing  bulldog 
forceps  on  the  free  ends.  The  nerves  must  be  frequently  moistened  with  0.9  per 
cent,  saline. 

87 


EXPERIMENTAL  PHYSIOLOGY. 


upper  part  of  the  cut  nerve.  Stimulate  with  an  interrupted  current 
of  moderate  strength  and  watch  the  effect  on  the  vessels  and  pupils. 
If  no  change  occurs,  repeat  with  the  other  nerve.  The  nerve  which 


FIG.  26.  Dissection  of  neck  of  rabbit  to  show  relative  position  of  nerves, 
etc.:  (c)  carotid  artery;  (ft)  vagus;  (5)  sympathetic;  (d)  cardiac  depressor;  (m) 
descending  branch  of  hypoglossal  nerve.  (After  Jackson). 

causes  definite  effects  is  the  sympathetic.  Explain  the  causes  of 
the  results.  It  is  often  advisable  to  introduce  the  tracheal  and 
carotid  cannulae,  as  directed  under  par.  3,  before  attempting  to 
stimulate  the  nerves. 


VASO  MOTOR  NERVES.  +     89 


/J& 


3.  DEMONSTRATE  THE  EFFECT  OF  STIMULATION  OF  THE  VAGUS 
NERVE  ON  THE  ARTERIAL  BLOOD  PRESSURE.  —  Introduce  tracheal 
and  carotid  cannulae  as  described  in  pars.  2,  and  3  (Exp.  35),  and 
apply  electrodes  to  the  peripheral  end  of  the  vagus.  Take  about 
an  inch  of  normal  tracing  and  cut  the  vagus  on  one  side  while  a 
tracing  is  being  taken.  Note  any  effect  on  the  blood  pressure. 
Apply  electrodes  to  the  peripheral  end  of  the  cut  vagus  and  stimu- 
late with  an  induced  current  of  moderate  strength  (just  bearable  to 
the  tip  of  the  tongue).  Repeat  with  stimuli  of  varying  strengths. 
Remove  the  electrodes  to  the  central  end  of  the  vagus  and  repeat 
the  stimulation. 


FIG.  27.  Stimulation  of  the  cardiac  depressor  nerve  in  the  rabbit,  showing 
effect  on  arterial  blood  pressure.  In  the  tracing  to  the  right  the  vagi  were  intact; 
in  the  tracing  to  the  left  they  were  cut.  Note  the  slower  respiratory  oscillations 
after  cutting  the  nerve. 

In  the  above  experiments,  the  drum  should  be  revolving  slowly 
while  the  stimuli  are  applied,  and  the  moments  at  which  this  is 
done  should  be  indicated  by  short-circuiting  the  time  tracing. 
Explain  the  causes  of  the  results. 

4.  DEMONSTRATE  THE  EFFECT  OF  STIMULATION  OF  THE  DE- 
PRESSOR NERVE  ON  THE  BLOOD  PRESSURE. — Pick  up  the  ligature 
tied  to  the  central  end  of  the  depressor  nerve  (the  small  nerve 
which  is  not  the  sympathetic),  apply  electrodes  and  stimulate. 
A  fall  in  blood  pressure  should  occur  (Fig.  27).  Look  for  slowing 
of  the  heart.  Show  that  the  fall  in  blood  pressure,  caused  by 
stimulation  of  the  depressor,  is  not  entirely  due  to  reflex  vagus 


90  EXPERIMENTAL  PHYSIOLOGY. 

inhibition,  since  it  persists  after  both  vagi  are  severed.  What  con- 
clusions do  you  draw  as  to  the  cause  of  the  fall?  Finally  stimulate 
the  peripheral  ends  of  the  depressor  and  sympathetic  nerves. 
The  sympathetic  stimulation  sometimes  quickens  the  heart. 

5.  ESTIMATE  THE  CIRCULATION  TIME  FOR  THE  LESSER  CIRCU- 
LATION (Stewart's  method). — Ligate  the  carotid  and  remove  the 
cannul^.    On  the  same  side  of  the  neck  insert  a  cannula  (pointing 
towards  the  heart)  in  the  jugular  vein    (for  technique  see  par.  6, 
Exp.  31).    Expose  the  carotid  artery  of  the  opposite  side  and  place 
under  it  a  strip  of  white  glazed  paper  resting  on  a  piece  of  thin 
rubber  dam.  Throw  a  strong  light  on  the  artery.   Connect  the  venous 
cannula  with  a  burette  containing  a  0.2%  solution  of  methylene 
blue  in  physiological  saline  solution,  at  the  temperature  of  the 
body.    See  that  there  is  no  air  in  the  tubing.     When  all  is  ready, 
remove  the  bull-dog  forceps  and  mark  the  exact  moment  that  the 
methylene  blue  enters  the  vein  (i.e.,  when  the  methylene  blue  is 
seen  through  the  cannula  to  enter  the  vein).    Carefully  observe  the 
carotid  artery.    The  moment  at  which  the  blue  appears  in  the  artery 
is  also  noted.    Repeat  several  times,  using  always  the  same  amount 
of  methylene  blue.    To  obtain  accurate  results  no  methylene  blue 
solution  should  be  allowed  to  escape  on  to  the  wound.    The  results 
are  to  be  given  in  relationship  to  (1)  actual  periods  of  time  and 
(2)  the  heart-beats. 

6.  DETERMINE  THE  SEAT  OF  OXIDATION  IN  THE  BODY. — Inject 
an  excess  of  a  stronger  solution  of  methylene  blue  until  the  animal 
is  killed  by  the  injections,  and  make  a  careful  autopsy;  examining 
especially  sections  of  the  muscles,  kidneys  and  liver,  also  the  urine, 
the  blood  in  the  mesenteric  vessels,  etc.    The  methylene  blue  will 
be  found  to  have  stained  the  blood  but  not  the  tissues.    The  tissues 
have  reduced  it  to  methylene  white.     This  is  known  as  Ehrlich's 
experiment  and  it  shows  that  the  tissues  are  the  seat  of  reduction 
in  the  body.     Note  the  effect  which  exposure  to  air  has  on  the 
colour  of  the  cut  organs.     On  standing  exposed  to  the  air  the  cut 
tissues  will  become  blue  because  of  oxidation  of  the  methylene 
white  to  methylene  blue.     What  conclusions  do  you  draw  from  the 
experiment? 


VASO  MOTOR  NERVES.  91 

COAGULATION  OF  BLOOD. 

Experiment  37. — A.  Expose  the  carotid  artery  and  jugular  vein 
in  an  anesthetized  rabbot.  Treat  each  as  follows :  Tie  a  ligature 
around  the  vessel  as  close  to  the  heart  as  possible.  When  rilled 
with  blood  tie  a  second  ligature  2  cm.  above  the  first,  and  a 
third  2  cm.  above  the  second.  Crush  the  vessel  between  the 
first  and  second  ligature  by  means  of  a  hemostat  without 
rupturing  the  wall.  Later,  when  the  rest  of  the  experiment  is 
completed  look  for  an  intravascular  clot  in  each  vessel  "  pocket." 
Explain. 

B.  Insert  a  cannula  into  the  carotid  artery  of  the  other  side, 
Draw  5  c.c.  of  blood  into  each  of  the  test  tubes  prepared  as 
follows,  after  which,  the  time  required  for  the  first  appearance 
of  a  clot  is  determined. 

1.  Clean — keep  at  room  temperature. 

2.  Clean— keep  at  37°  C.  to  40°  C. 

3.  Clean-keep  at  0°  C.  to  5°  C. 

4.  Containing  sand  with  which  the  blood  is  to  be  shaken. 

5.  Thoroughly  coated  inside  with  a  vaseline  or  paraffin  oil. 

6.  Containing  a  small  amount  of  potassium  oxalate  with 

which  the  blood  is  to  be  shaken.  After  ascertaining 
that  oxalated  blood  does  not  clot  add  a  drop  or  two 
of  5%  CaCl2  solution,  increasing  the  quantity  if 
necessary. 

7.  Vaselined — centrifuge  the    blood,  separating  the  plasma 

and  keeping  it  for  observation. 

C.  Several  glass  tubes  from  3  to  4  cm.  long  (3  to  4mm.  dia.) 
and    tapere'd   nearly   to   capillary   dimensions   at   one   end   are 
oiled  inside.     A  short  length  of  rubber  tubing  is  doubled  at 
one  end  and  tied  with  thread.     This  tube  should  fit  easily  but 
snugly  to  the  glass  tubes  and  is  used  as  a  pipette  bulb  to  suck 
blood  into  the  glass  tubes. 

A  rabbit's  ear,  with  hair  closely  clipped  and  washed  thor- 
oughly long  enough  before  to  permit  drying,  is  oiled.  When 
the  observer  is  ready  to  note  the  time,  a  vein  is  punctured  by 
holding  the  under  surface  of  the  ear  against  a  cork  and  plunging 
a  sharp  three-cornered  needle  through  it.  Four  samples  of 


92  EXPERIMENTAL  PHYSIOLOGY 

blood  are  drawn  up  into  the  glass  tubes.  The  first  appearance 
of  a  clot  is  determined  by  drawing  out  a  small  glass  rod.  Each 
tube  must  have  its  own  rod.  From  time  to  time  (every  20  to 
30  sees.)  the  rod  is  to  be  inserted  and  the  first  clot  sought. 

After  having  become  practised  in  the  method  blood  is  drawn 
from  the  human  ear  or  finger  and  the  clotting  time  determined. 
In  the  case  of  the  finger,  it  should  be  exercised  for  several 
seconds,  then  a  handkerchief  wrapped  tightly  around  it  at  the 
second  joint,  the  first  joint  being  bent  at  a  right  angle.  The 
skin  is  punctured  now  a  little  below  the  base  of  the  nail. 

In  every  subject  three  determinations,  which  check  within 
the  limits  of  experimental  error,  should  be  made.  Obtain 
observations  from  as  many  different  subjects  as  possible. 

D.  Place  a  drop  of  human  blood  or  rabbit's  blood  on  a 
slide  and  cover  with  a  cover-slip.  Observe  the  blood  with  a 
microscope  from  time  to  time  so  that  the  fine  structure  and 
behaviour  of  a  clot  may  be  seen.  Between  observations  cover 
the  slide  with  a  moist  chamber  cover  containing  wet  filter  paper 
plastered  to  the  inside;  otherwise  the  blood  will  dry  before  it 
clots. 

Summarize  the  information  which  you  have  obtained  form 
the  above  experiments. 


CHAPTER    IX.* 

POLYSPHYGMOGRAPH  TRACINGS. 

These  experiments  consist  in  obtaining  graphic  records  of  the 
pulses  of  the  radial  and  carotid  arteries,  of  the  apex  beat  and  of  the 
venous  pulse  in  the  jugular  vein.f 

The  experiments  are  important  not  only  because  the  results 
if  properly  interpreted  throw  much  light  on  the  cardio-vascular 
mechanism,  but  because  of  the  value  of  the  technique  in  clinical 
diagnosis.  The  tracings  are  often  difficult  to  obtain,  and  great 
care  and  patience  must  be  exercised  in  adjusting  the  various  re- 
ceiving tambours.  This  is  especially  so  for  the  radial  pulse  and 
apex  beat.  When  these  two  cannot  be  satisfactorily  obtained  to- 
gether, the  carotid  should  be  substituted  for  the  radial.  The  ob- 
served person  must  remove  his  shirt  and  lie  on  a  couch  or  table. 
Sometimes  it  is  best  to  lie  on  the  side,  sometimes  on  the  back. 
While  cardiac  tracings  are  being  taken,  the  breath  should  be  held 
for  a  few  moments. 

Experiment  38. 

A.  The  Velocity  of  Transmission  of  the  Pulse  Wave.  (Pro- 
pagation of  Pulse  Wave). — With  the  arm  easily  extended  and 
resting  on  the  arm  support,  apply  the  button  of  the  receiving  tam- 
bour over  the  radial  artery  and  adjust  the  pressure  until  a  maximal 
movement  of  the  recording  lever  is  observed.  Taking  care  that  the 
radial  tambour  does  not  slip,  now  apply  the  carotid  tambour  by 
hand  (apply  opposite  the  angle  of  the  jaw).  When  a  maximal 
pulsation  of  both  of  the  levers  is  obtained,  adjust  the  writing  points 
to  a  slowly  moving  clockwork  drum.  The  writing  points  should  be 
as  nearly  as  possible  in  the  same  perpendicular,  and  should  be 

*For  the  experiments  of  this  chapter  two  sessions  of  three  or  four  hours  each 
are  necessary. 

fNotes  and  tracings  of  these  experiments  are  to  be  taken  by  every  member 
of  the  class. 

93 


94 


EXPERIMENTAL  PHYSIOLOGY 


applied  to  the  drum  with  a  minimal  amount  of  friction.  This  is 
done  by  manipulating  the  adjusting  screws  on  the  tambour  stands, 
while  the  drum  is  moving  slowly.* 

When  the  adjustment  is  completed  the  drum  is  stopped  for  a 
moment  so  that  the  two  levers  may  draw  vertical  lines  showing 
their  relative  positions  (alignment  marks).  The  drum  is  then 
allowed  to  revolve  at  a  medium  speed  and  the  tracings  taken. 
The  speed  should  be  as  great  as  is  consistent  with  a  definite  up- 
stroke of  the  pulse.  Alignment  marks  should  be  inscribed  at 
frequent  intervals  (by  stopping  the  drum  for  a  moment).  A  time 
record  (0.2  sec.)  is  added  to  the  tracing  with  the  drum  revolving  at 


FIG.  28.  Simultaneous  tracings  of  carotid  and  radial  pulses.  The  rate  of 
transmission  is  determined  by  finding  the  difference  between  the  beginning  of 
each  pulse,  after  correcting  for  alignment  of  levers,  and  measuring  off  this  distance 
on  the  time  tracing  (l/50ths  second.). 


the  same  speed  as  when  the  pulse  tracings  were  being  taken.  A 
vibrating  spring  provided  with  a  writing  point  is  used  for  taking 
the  time  tracing. 

After  the  removal  of  the  tracing  from  the  drum,  the  distance  of 
the  beginning  of  the  upstroke  is  measured  from  its  alignment  mark 
for  each  pulse  curve  (Fig.  28).  The  difference,  interpreted  in  terms 
of  the  time  tracing,  gives  the  rate  at  which  the  pulse  wave  travels 
from  the  carotid  to  the  radial  artery.  Note  also  the  dicrotic  notch 

This  is  more  satisfactory  than  attempting  to  adjust  to  a  stationary  drum 
because  friction  is  diminished.  Before  starting  the  drum,  however,  make  certain 
that  the  tambours  are  so  adjusted  as  to  give  the  greatest  possible  movements. 


POLYSPHYGMOGRAMS.  95 

and  measure  its  distance  from  the  beginning  of  the  upstroke. 
Several  measurements  should  be  taken  from  each  member  of  the 
group.  How  can  the  length  of  the  pulse  wave  be  calculated? 

In  the  more  or  less  arbitrary  lettering  of  the  waves  observed  in 
pulse  tracings,  the  main  upstroke  is  marked  3,  in  the  case  of  the 
carotid  and  4  in  that  of  the  radial ;  the  dicrotic  notch  of  the  carotid 
is  5  and  of  the  radial  6.  The  distances  between  3  and  5  and  be- 
tween 4  and  6  represent  respectively  the  time  during  which  the 
heart  is  pumping  blood  into  the  arteries,  i.e.,  the  semilunar  valves 
are  open.  It  is  called  the  sphygmic  period  ui  period  E. 

B.  The  Venous  or  Jugular  Pulse  Curve. — Have  the  observed 
person  lie  down  with  his  head  slightly  raised  by  a  cushion  and  bent 
to  the  right  side.  Place  the  receiver  (thistl"  funnel)  over  the  jugular 
bulb  on  the  right  side  of  the  neck.  This  lies  immediately  above 
the  inner  end  of  the  clavicle.  Bring  the  point  of  the  lever  of  the 
recording  tambour  to  write  with  a  minimal  amount  of  friction  on 
a  drum.  Since  a  venous  pulse  tracing  cannot  be  interpreted  with- 
out a  simultaneous  tracing  from  an  artery,  adjust  the  button  of  a 
receiving  tambour  over  the  radial  artery  and  arrange  the  writing 
style  of  its  recording  tambour  so  as  to  write  on  the  drum  in  the 
same  perpendicular  as  the  style  of  the  venous  tambour.  If  no 
satisfactory  tracing  can  be  secured  from  the  radial,  try  the  carotid. 
Remember  to  inscribe  alignment  marks  at  short  intervals.  While 
the  tracing  is  being  taken  it  is  usually  advisable  that  the  respiratory 
movements  be  suspended. 

To  INTERPRET  THE  VENOUS  CURVE. — Make  a  vertical  mark 
on  the  arterial  pulse  tracing  corresponding  to  the  beginning  of 
the  pulse  upstroke.  If  this  is  done  on  the  radial  pulse  tracing, 
measure  1/10  sec.  in  front  of  it  and  make  another  vertical  mark. 
(This  mark  is  to  allow  for  the  time  lost  in  propagation  of  pulse  from 
heart  to  radial.  It  is  determined  according  to  Exp.  A). 

This  line  3  corresponds  to  the  beginning  of  the  sphygmic  period 
of  ventricular  systole,  i.e.,  to  the  opening  of  the  semilunar  valves. 
Measure  the  distance  from  line  3  to  the  nearest  alignment  mark. 
By  measuring  off  the  same  distance  from  the  corresponding  align- 
ment mark  of  the  venous  tracing  line  3  will  be  found  to  fall  at  the 
beginning  of  a  small  wave  which  is  marked  c.  The  small  wave  in 
front  of  c  is  marked  a  and  is  due  to  auricular  systole.  The  large 


96  EXPERIMENTAL  PHYSIOLOGY. 

wave  of  depression  following  c  is  marked  x  and  is  due  to  a  fall  of 
pressure  in  the  auricle.  What  causes  this  fall  in  pressure? 

The  next  point  to  determine  is  the  end  of  the  sphygmic  period. 
This  is  found  by  measuring  from  the  alignment  mark  to  line  5  of 
the  carotid  or  line  6  of  the  radial  (less  1/10  sec.)  and  transferring 
to  the  jugular  tracing.  The  line  will  be  found  to  fall  on  a  small  wave 
on  the  upstroke  of  the  depression.  This  wave  is  marked  V  and  is 
due  to  the  sudden  opening  of  the  tricuspid  valves.  Sometimes 
another  small  wave  just  precedes  V.  It  corresponds  to  closure  of 
the  semilunar  valves.  Listen  to  the  heart  sounds  while  recording 
a  tracing  in  order  to  determine  this  fact. 

In  preparing  your  report  of  the  experiment,  draw  in  the  intra- 
auricular  and  intra-ventricular  pressure  curves  in  relationship  to 
the  venous  curve. 

C.  Cardiograms. — Apply  the  button  of  the  special  receiving 
tambour  to  the  apex  beat  and  connect  with  a  recording  tambour. 
Adjust  the  position  and  pressure  of  the  button  until  a  maximal 
movement  of  the  writing  style  of  the  recording  tambour  is  obtained^ 
Apply  the  writing  point  to  a  carefully  levelled  drum  and  with  this 
running  at  moderately  high  speed,  take  a  tracing.  There  is  often 
difficulty  in  securing  a  satisfactory  tracing,  and  it  may  be  necessary 
to  try  another  subject.  Breathing  should  be  suspended  for  a  few 
moments  while  the  tracing  is  being  taken. 

To  INTERPRET  THE  CURVE. — Adjust  another  receiving  tambour 
to  the  radial  or  carotid  pulse  with  both  writing  styles  in  the  same 
perpendicular,  and  following  the  other  directions  described  under 
"Venous  Pulse",  mark  on  the  cardiogram: 
-   1.  The  beginning  of  the  sphygmic  period,  E  (line  3). 

2.  The  end  of  the  sphygmic  period,  E  (line  5). 

3.  The  auricular  wave  (beginning  of  this  wave  is  line  1;  the 

end  of  it,  line  2). 

4.  The  beginning  of  ventricular  systole  (difference  between  2 

and  3  equals  the  presphygmic  interval). 

5.  The  opening  of  auriculo-ventricular  valves  (lowest  point  in 

tracing;  somewhat  difficult  to  determine). 

When  satisfactory  tracings  have  been  secured  apply  a  stethoscope 
to  the  apex  beat  and  after  accustoming  your  ear  to  the  sounds,  mark 
as  accurately  as  possible,  by  free  hand,  the  position  on  the  cardio- 


POLYSPHYGMOGRAMS.  97 

gram  at  which  they  are  heard.  The  second  (sharp)  sound  can  be 
heard  best  over  the  sternal  end  of  the  second  rib  on  the  right  side. 

.Influence  of  Respiratory  Movements  on  the  Various  Pulse 
Tracings. — Apply  the  respiratory  tube  to  the  thorax  and  connect 
with  a  recording  tambour.  Also  arrange  to  take  a  tracing  of  one 
or  the  other  of  the  pulses,  or  of  the  heart  beat.  Record  simultaneous 
tracings  of  the  respiratory  movements  and  of  the  pulse.  Note  the 
effect  of  inspiration  and  expiration  respectively  on  the  pulse  curves. 

How  do  you  explain  the  effects? 

TESTING  CARDIAC  EFFICIENCY. 

Experiment  39. — Count  the  pulse  arid  the  respirations  and  record 
the  systolic  and  diastolic  blood  pressures  of  a  person  while 
sitting.  Then  have  him  stand  up  and  raise  a  pair  of  dumbbells 
from  the  floor  to  the  level  of  the  shoulders  with  the  arms  ex- 
tended, at  a  rate  of  30  times  a  minute,  and  continue  the  exercise 
for  2  minutes.  Immediately  the  exercise  is  discontinued  again 
repeat  the  above  observations  and  continue  doing  so  at  intervals 
during  the  recovery  period,  until  all  the  observed  values  have 
returned  to  normal  levels.  It  will  be  necessary  to  repeat  the 
muscular  exercise  several  times,  in  order  to  obtain  a  sufficient 
number  of  observations  from  which  to  obtain  a  complete 
picture  of  the  after  effects.  It  is  most  important  that  this  be 
done  carefully  since  it  has  been  *found  that  by  such  methods 
the  functional  capacity  of  the  heart  can  best  be  guaged  (cf. 
Cotton,  Rapport,  and  Lewis,  Heart,  6,  269). 

Besides  obtaining  the  data  indicated  above  also  make 
careful  observations  on  the  following:  (a)  The  precise  moment 
at  the  start  of  exercise  at  which  the  breathing  and  pulse  rate 
became  changed,  (b)  The  length  of  the  period  following  exer- 
cise during  which  the  pulse  rate  and  blood  pressure  remain 
changed,  (c)  The  con  tour  of  the  arterial  pulse  curve  before  and 
after  the  exercise.  To  obtain  this  tracing  the  Dudgeon  sphymo- 
graph  may  be  used.  Note  particularly  whether  a  dicrotic  wave 
appears,  (d)  :The  tension  of  CO2  in  the  alveolar  air.  The 
samples  must  be  collected  during  and  as  early  after  the  exercise 
as  possible.  (Since  only  two  or  three  pieces  of  apparatus  are 
available  for  these  analyses  the  various  groups  must  arrange 
their  experiments  so  that  this  observation  can  be  made  by  all.) 
xThis  observation  is  to  be  made  only  after  Experiment  has  been  performed. 


SECTION    III. 
THE  CENTRAL  NERVOUS  SYSTEM. 

CHAPTER    X. 
R*EFLEX  ACTION  IN  THE  FROG. 

In  a  nerve  fibre  impulses  are  transmitted  with  equal  facility  in 
either  direction  (Exp.  18,  p.  45),  but  in  a  reflex  arc  they  go  in  one 
direction  only.  The  nerve  centre  is  responsible  for  this  directive 
influence,  and  the  centre  may  be  situated  either  peripherally,  as  in 
ganglia,  or  centrally,  as  in  the  brain  and  spinal  cord.  The  exact 
significance  of  the  centres  in  the  brain  and  spinal  cord  varies  con- 
siderably in  different  animals  according  to  their  degree  of  develop- 
ment. In  a  general  way  the  centres  in  the  spinal  cord  are  primarily 
the  local  centres  for  each  segment  of  the  body,  but  the  reflex 
activities  of  other  segments  may  be  caused  to  cooperate  so  as  to 
bring  about  complex  movements.  The  centres  in  the  brain,  on  the 
other  hand,  are  to  be  regarded  as  affording  higher  nervous  path- 
ways which  the  reflex  impulse  does  not  necessarily  traverse,  but 
in  which,  when  it  does  so,  considerable  modification  may  occur. 
The  impulse  may,  for  example,  become  suppressed  (inhibited)  or 
exaggerated  (augmented)  by  its  passage  through  nerve  centres  in 
which  memory  impressions  have  been  stored  away.  If  these 
memory  impressions  indicate  that  reflex  movements  would  be 
harmful  to  the  animal  then  the  movements  may  be  inhibited:  under 
the  converse  conditions  thay  may  be  augmented.  On  account  of 
this  dominating  influence  of  the  higher  over  the  lower  centres  it  is 
clear  that  a  precise  analysis  of  the  physiology  of  reflex  action 
demands  a  simplification  of  the  experimental  conditions,  by  iso- 
lating the  spinal  cord  from  the  brain.  In  the  lower  vertebrates 
this  can  readily  be  done  by  actually  removing  or  destroying  the 
latter.  In  the  higher  vertebrates,  this  operation  is  incompatible 
with  life,  so  that  the  brain  is  merely  isolated  from  the  spinal  cord 
by  cutting  the  latter  below  the  level  of  exit  of  the  nerves  to  the 
chief  respiratory  muscles  (diaphragm).  This  so-called  SPINAL 

9* 


CENTRAL  NERVOUS  SYSTEM.  99 

ANIMAL  offers  a  most  suitable  preparation  for  the  study  of  reflex 
activities.  Immediately  following  its  isolation  from  the  brain  the 
cord  enters  into  a  depressed  condition  called  SPINAL  SHOCK.  This 
is  quickly  recovered  from  in  the  lower  animals,  but  may  take 
months  to  disappear  in  the  higher. 

Experiment  40. — Pith  a  frog,  destroying  the  brain  only  and  sus- 
pend the  animal  by  fixing  the  lower  jaw  to  a  clamp  (Fig.  29). 
Apply  mechanical  stimuli  (by  pinching)  to  the  skin  of  various 
regions  and  note  the  location  and  character  of  the  response. 
Commence  the  application  of  the  stimuli  immediately  after 
decerebration  and  observe  by  repeating  at  intervals  whether 
they  improve  with  time.  If  they  do  so,  what  is  your  conclusion  ? 
Proceed  now  to  demonstrate  the  duration  of  the  latent  period  or 
reflex  time  using  as  the  stimulus  a  0.1  per  cent,  solution  of  HoSO4. 
Measure  accurately  the  time  which  elapses  between  placing  the 
foot  in  the  acid  and  the  movement  of  the  leg.  Remove  all 
traces  of  acid  from  the  skin  by  means  of  water.  Make  three 
observations  with  the  same  strength  of  acid  using  the  two  feet 
alternately  and  allowing  some  time  (several  minutes)  to  elapse 
between  the  stimulations.  Repeat  the  observations  using  0.3 
per  cent.  acid.  Are  any  differences  in  latent  period  and  in- 
tensity of  response  observed,  depending  on  the  strength  of 
stimulus? 

It  is  likely,  with  the  strong  stimuli  employed  in  the  above 
experiments,  that  some  spread  (or  irradiation)  will  have  occurred 
in  the  cord,  so  that  the  opposite  hind  limb  or  the  fore  limbs 
show  movements.  How  is  this  explained? 

Experiment  41. — To  investigate  the  "march"  of  the  irradia- 
tion more  precisely  and  to  demonstrate  that  the  isolated  cord 
is  capable  of  synthesising  a  complicated  and  apparently  pur- 
poseful group  of  movements  saturate  a  piece  of  filter  paper  in 
30  per  cent,  acetic  acid,  remove  the  excess  of  acid  and  place  a 
small  square  of  this  paper  on  one  of  the  flanks  of  the  frog. 
After  noting  the  character  of  the  movements,  wash  away  the 
acid  and  repeat,  holding  the  leg  on  the  irritated  side. 
The  Spreading  of  Reflexes  in  the  cord  is  greatly  facilitated  by 
strychnine,  but  the  movements  are  not  of  the  same  "purposeful" 
character  as  those  just  studied. 


100 


EXPERIMENTAL  PHYSIOLOGY. 


FIG.  29.    Decerebrate  frog  suspended  for  studying  reflex  action. 


CENTRAL  NERVOUS  SYSTEM. 


101 


Experiment  42. — Inject  a  few  drops  of  a  0.5  per  cent,  solution  of 
strychnine  sulphate  into  the  dorsal  lymph  sac  of  the  frog.  Apply 
weak  stimuli  at  intervals  to  the  skin  of  different  parts  of  the 
body  and  note  the  exact  nature  of  the  responses.  Explain  the 
action  of  the  strychnine. 
Inhibition  of  Reflexes. — Reflex  activities  may  be  inhibited 

either  through  afferent  nerves  or  from  the  higher  centres. 


FIG.  30.     Exposed   brain  of  frog:    (c)  cerebrum;   (o)    optic  lobes; 
(d)  cerebellum;  (e)  medulla. 


Experiment  43. — Expose  the  sciatic  nerve  in  the  left  thigh.  Tie 
a  ligature  about  the  nerve  near  the  knee  and  cut  the  nerve 
distal  to  the  ligature.  Immerse  the  right  leg  of  the  frog  in 
0.5%  sulphuric  acid  and  note  the  latent  period  for  reflex  action. 
Immediately  wash  off  the  acid.  After  three  minutes  place 
electrodes  on  the  exposed  sciatic  nerve  and  as  the  right  foot  is 
again  immersed  in  the  acid,  stimulate  the  nerve  with  a  weak 
tetanizing  current.  Prove  that  the  sensory  endings  in  the  skin 
are  still  irritable  by  the  acid.  Explain  the  inhibition. 


102  EXPERIMENTAL  PHYSIOLOGY. 

To  show  that  reflexes  can  be  inhibited  by  influences  from 
higher  centres,  place  a  crystal  of  salt  on  the  optic  lobes  which 
have  been  exposed  in  a  live  frog  by  quickly  cutting  off  the  anterior 
portion  of  the  head  just  behind  the  tympani  with  heavy  scissors 
(Fig.  30).  Now  attempt  to  elicit  reflexes  by  the  methods  described 
above. 

THE   FUNCTION    OF   THE    SPINAL    NERVE    ROOTS. 

Experiment  44. — Pith  the  brain  of  a  large  frog  and  fasten  it  ventral 
side  down.  Slit  and  evert  the  skin  over  the  last  four  vertebrae; 
remove  the  muscles  from  the  vertebral  arches  and  then  open 
the  spinal  canal  by  means  of  a  strong  scissors,  keeping  them 
close  to  the  bone.  Uncover  three  or  four  sets  of  roots.  Pass  a 
silk  ligature  under  a  dorsal  root  as  far  out  as  possible.  Tie  and 
cut  distal  to  the  ligature.  Stimulate  the  central  end  of  the  root. 
Tie  a  ligature  under  another  dorsal  root  close  to  the  cord  and 
cut  the  root  central  to  it.  Now  stimulate  distal  to  the  ligature. 
In  like  manner  test  the  function  of  the  ventral  roots.  In  this 
experiment  the  unipolar  method  of  stimulation  will  be  found 
best  because  of  the  shortness  of  the  spinal  roots.  The  plate 
electrode,  attached  by  a  wire  to  the  secondary  coil  is  placed 
in  contact  with  the  belly  of  the  frog.  The  other  wire  is  con- 
nected with  a  dissecting  needle  which  then  serves  as  the  more 
active  electrode  to  stimulate  the  nerve  roots.  Note  the  nature 
of  the  movements  produced  in  the  above  experiments  and  draw 
a  diagram  showing  the  functions  of  the  roots. 

THE  FUNCTIONS  OF  THE  CEREBRUM  IN  THE  FROG. 

Interesting  observations  can  be  made  on  a  decerebrate  frog, 
but  it  must  be  remembered  that  they  do  not  shed  much  light  on 
the  functions  of  the  cerebrum  in  the  higher  mammals  because  in 
these  the  cerebral  centres  are  relatively  far  more  important  and 
participate  in  many  reflex  activities  in  which  the  spinal  cord  alone 
is  involved  in  lower  animals. 

Experiment  45.— Activities  of  a  Decerebrate  Frog.— Anaesthe- 
tize a  frog  by  placing  it  under  a  beaker  together  with  a  piece 


CENTRAL  NERVOUS  SYSTEM  103 

of  absorbent  cotton  containing  ether.  Slit  and  retract  the  skin 
over  the  skull  and  remove  a  triangular  piece  of  the  latter  so  as 
to  expose  the  cerebrum.  The  base  of  the  triangle  should  be 
on  a  line  connecting  the  posterior  border  of  the  tympanic 
membranes  and  should  be  about  a  centimeter  wide.  Avoid 
injury  to  the  brain  beneath  until  the  cerebrum  is  completely 
exposed,  then  carefully  remove  the  latter  and  plug  the  cavity 
loosely  with  cotton.  Sew  the  skin  in  place  and  keep  the  animal 
where  the  skin  will  remain  moist  until  the  next  day.  This 
can  be  done  by  placing  the  frog  with  a  little  water  in  an  evaporat- 
ing dish  and  covering  all  with  a  large  funnel  or  something  which 
will  prevent  escape,  but  at  the  same  time  allow  access  of  plenty 
of  air. 

After  24  hours  study  the  behaviour  of  the  decerebrate 
animal  compared  with  a  normal  frog,  noticing  especially: 
posture,  ability  to  swim  or  hop,  power  of  escaping  from  a  vessel 
of  water  gradually  heated,  ability  to  turn  over  when  placed  on 
the  back. 

Again  open  the  cranial  cavity,  without  anaesthesia  as  there 
can  be  no  sense  of  pain,  and  destroy  the  corpora  stria ta  and 
optic  thalami.  After  recovery  from  shock  observe  the  activities 
as  before.  Finally  destroy  the  rest  of  the  brain  and  notice  any 
change  in  behaviour. 


CHAPTER   XI. 

REFLEX  ACTION  IN  MAN. 

There  are  in  general  three  types  of  reflexes  elici table  in  man  and 
the  higher  mammals.  These  are:  1.  The  reflex  movements  pro- 
duced by  the  application  of  hurtful  or  nocuous  stimuli  to  the  skin 
(nociceptive  reflexes).  2.  The  reflexes  required  to  maintain  the 
joints  in  such  a  position  that  the  animal  may  stand  erect  and  move 
about  (postural  reflexes).  3.  So-called  myotatic  reflexes  which  are 
contractions  produced  by  direct  mechanical  stimulation  of  muscles 
that  have  been  brought  into  a  hyperexcitable  condition  (hyper- 
tonus)  through  reflex  action. 

An  example  of  nociceptive  reflexes  is  the  flexion  reflex  already 
studied  in  the  spinal  frog.  In  man  this  type  of  reflex,  variously 
modified  according  to  the  part  of  the  body  from  which  it  is  elici- 
ted, is  extensively  employed  in  the  diagnosis  of  nervous  diseases. 
The  particular  value  of  the  reflex  is  that  its  presence  or  absence 
indicates  the  condition  of  the  reflex  pathway  at  the  various  levels. 
For  the  study  of  reflex  time  it  is  useful  to  employ  the  palpebral 
reflex,  but  in  doing  so  it  must  be  remembered  that  there  are  several 
fundamental  differences  between  this  and  the  flexion  reflex,  such 
as  the  relationship  between  strength  of  stimulus  and  latent  time  as 
well  as  intensity  of  response. 

Experiment  46. — By  means  of  a  strip  of  adhesive  tape  attach  a 
thread  to  the  upper  eyelid.  Pass  the  thread  through  the  handle 
of  scissors  which  have  been  clamped  to  a  stand  to  serve  as  a 
pulley.  Attach  the  thread  to  a  heart  lever.  The  head  should 
be  held  firmly  in  such  a  position  that  when  the  upper  eyelid 
is  closed  the  writing  point  of  the  lever  moves  upward.  To  elicit 
the  reflex  the  subject  presses  a  pair  of  electrodes  against  the 
lower  lid.  The  operator  stimulates  the  subject  with  break 
shocks  only,  using  a  current  which  is  just  strong  enough  to  cause 
the  upper  lid  to  move.  The  subject  must  not  see  the  operator 
at  work.  With  the  aid  of  a  magnetic  signal  determine  the  reflex 
time  on  a  rapid  clock-work  drum.  Calculate  the  average  reflex 

104 


REFLEX  ACTION. 


105 


time    from  a  number  of  observations  on   the  same    subject. 

Each  individual  of  the  pair  should  serve  as  subject. 

There  is  no  example  of  a  postural  reflex  which  can  conveniently 
be  studied  in  the  frog  or  man.  (The  extensor  thrust  and  the  mark- 
time  reflexes  (see  p.  240)  of  the  spinal  mammal  will  serve  this 
purpose) . 

The  myotatic  reflexes  are  best  illustrated  in  the  KXEE  JERK. 


FIG.  31.     Arrangement  of  apparatus  for  measurement  of  reaction  time  in  man. 

Experiment  47. — Let  the  subject  sit  in  a  comfortable  position  with 
one  leg  crossed  over  the  other  so  that  the  patellar  ligament  is 
under  an  increased  tension.  The  operator  strikes  the  patellar 
ligament  a  sharp  blow  with  the  edge  of  his  hand  or  a  book. 
With  a  little  practice  it  is  easy  to  elicit  a  sudden  contraction 
of  the  quadriceps  muscle  giving  a  sudden  extension  of  the  leg. 


106  EXPERIMENTAL  PHYSIOLOGY. 

This  should  be  tried  on  a  number  of  subjects.  After  observing 
the  extension  in  each  subject,  try  the  effect  of  REINFORCEMENT 
by  the  following  methods: 

1.  Clenching  the  hands  together  vigorously. 

2.  Strong  sensory  stimulation  such  as  pulling  the  hair. 

3.  Mental  effort  as  solving  a  problem. 

The  magnitude  of  the  response  seems  to  depend  on  the  tone 

of  the  muscle. 

Tone  depends  on  the  condition  of  the  nervous  system,  therefore 
the  knee  jerk  is  an  important  means  of  ascertaining  certain  patho- 
logical conditions  of  the  central  nervous  system. 

REACTION  TIME  IN  MAN. 

Akin  to  reflex  latent  time  is  the  so-called  REACTION  TIME  in  man , 
that  is  the  time  which  elapses  between  the  application  of  a  stimulus 
and  a  prearranged  voluntary  reaction. 

Experiment  48. — In  this  experiment  the  apparatus  is  set  up  as  in 
Fig.  31.  With  the  operator's  key  A  open,  and  the  subject's  key 
B  closed,  the  operator  closes,  and  the  subject  opens  B  when- 
ever he  feels  the  stimulus.  The  signal  connected  with  the  keys 
writes  on  a  quickly  revolving  drum  on  which  a  time  tracing  in 
lOOths  of  a  second  is  also  inscribed.  Determine  the  average 
reaction  time.  Now  increase  the  stimulus  to  find  whether  the 
reaction  time  changes.  What  are  the  additional  factors  in- 
volved in  reaction  time  as  compared  with  reflex  time?  How  do 
different  subjects  vary? 


SECTION   IV. 
RESPIRATION. 

CHAPTER    XII. 
ANALYSIS    OF    AIR.      ALVEOLAR    AIR.      APNOEA. 

Experiment  49.— 

The  (Haldane)  gas  burette  A  (Fig.  32)  has  a  capacity  of  10  c.c.  of  which 
7  c.c.  are  contained  in  the  bulbar  portion  and  3  c.c.  are  on  the  tubular  portion. 

The  latter  is  graduated  to  —  ths  of  a  cubic  centimetre.    These  proportions 
100 

are  chosen  so  that  the  oxygen  in  atmospheric  air  may  be  measured.  The 
burette  is  connected  with  a  reservoir  containing  mercury  B  by  rubber  tubing 
of  sufficient  length  so  that  when  B  is  placed  on  the  upper  hook  (1)  the  mercury 
will  fill  the  burette.  On  this  tubing,  near  the  burette,  are  a  screw  clip  (a) 
and -a  pinch  cock  (b).  When  the  reservoir  is  hung  on  hook  (2)  the  mercury 
should  stand  at  the  10  c.c.  mark  in  the  burette.  At  the  upper  end  of  A  is 
a  three-way  stopcock  (c)  opening,  according  to  its  position,  either  with  the 
outside  or  into  a  side  tube  which  is  connected  by  thick  walled  rubber  tubing 
(g)  with  thfe  absorption  bulb  D.  On  the  tubing  above  the  bulb  is  a  much 
smaller  bulb,  E,  and  the  lower  end  of  the  absorption  bulb  is  attached  to  a 
reservoir,  F.  A  sufficient  amount  of  20  per  cent,  solution  of  NaOH  is  placed 
in  D  and  F  to  a  mark  on  the  tube  between  D  and  E.  The  gas  burette  is 
surrounded  by  a  water  jacket  and  the  whole  apparatus  is  mounted  on  a 
wooden  stand. 

As  described  the  apparatus  is  suitable  for  determination  of 
the  CO2  in  alveolar  air.  If  it  is  desired  also  to  determine  O2 
(either  in  atmospheric  or  alveolar  air)  the  absorption  apparatus 
shown  in  the  inset  of  Fig.  32  must  be  attached  at  the  joint  G. 
This  will  be  described  later. 

Analysis  for  CO2  alone.— The  first  step  is  to  test  the 
apparatus  for  leaks.  Turn  C  in  the  position  shown  in  I  so  that 
the  burette  communicates  directly  with  the  outside.  With 
both  screw  clip  (a)  and  pinch  cock  (b)  closed,  the  reservoir  is 
then  placed  on  hook  I,  after  which  first  a  and  then  b  are  partly 
opened  so  that  the  mercury  slowly  rises  in  the  burette  and 
displaces  the  faintly  acid  solution  with  which  it  was  left  filled. 

107 


108 


EXPERIMENTAL  PHYSIOLOGY. 


When  the  mercury  has  risen  to  the  piece  of  rubber  tubing  at 
the  end  of  tube  H,  b  is  closed  and  a  slowly  screwed  down  until 
the  mercury  just  fills  the  rubber  tubing  on  H  the  last  trace  of 
acid  water  being  removed  by  means  of  a  piece  of  filter  paper. 
The  next  step  is  to  lower  the  reservoir  B  to  hook  2,  release  the 
screw  clip  a  and  cautiously  open  clamp  b  so  that  the  mercury 


FIG.  32. 

slowly  falls  in  the  burette  to  a  little  below  the  10  c.c.  mark. 
The  tap  C  is  then  turned  in  the  position  III  so  that  both 
A  and  D  communicate  with  the  outside.  The  exact  position 
of  the  level  of  the  NaOH  solution  in  the  tube  between  D  and  E 
is  marked  on  the  glass  (by  a  glass  pencil  or  pen)  and  the  mercury 
level  in  the  burette  is  adjusted,  by  using  the  screw  clip  a,  so 


ALVEOLAR  AIR.  109 

that  the  dome  of  the  meniscus  stands  precisely  at  the  10  c.c. 
mark. 

The  tap  C  is  now  turned  so  that  A  and  D  are  alone  in  com- 
munication (as  shown  in  II)  and  the  reservoir,  B,  taken  off  the 
hook  by  the  left  hand  and  slightly  elevated,  after  which  a  is 
partly  unscrewed  and  b  held  open  by  the  right  hand.  The 
mercury  rises  in  A  so  that  the  air  passes  into  D  where  the  CO2 
is  absorbed  from  it.  By  cautiously  raising  and  lowering  B 
the  air  is  passed  several  times  (five)  between  A  and  D,  extreme 
care  being  taken  when  lowering  B  to  see  that  the  NaOH  solu- 
tion does  not  rise  into  the  narrow  tubing  d.  If  this  should 
happen,  or  a  broken  column  of  solution  get  into  the  tube  d, 
the  clamp  b  should  be  instantly  closed.  Finally,  the  clamp 
b  is  closed,  B  placed  on  hook  2  and  the  level  of  mercury  ad- 
justed by  using  b  and  a  until  the  NaOH  solution  stands  exactly 
at  the  original  level  in  d.  If  there  has  been  no  leakage,  the 
mercury  should  stand  precisely  at  the  10  c.c.  mark  (since 
atmospheric  air  contains  too  small  a  percentage  of  CO2,  0.03, 
to  be  measurable  in  such  a  burette). 

Having  thus  tested  the  reliability  of  the  apparatus,  analysis 
may  be  made  of  alveolar  air  collected  as  described  on  p.  110. 
To  transfer  the  gas  from  the  syringe  to  the  burette,  the  former 
is  attached  to  the  rubber  tubing  at  H  after  this  has  been  filled 
to  the  top  with  mercury,  as  described  above.  With  the  reservoir 
on  hook  2  and  the  clip  a  partly  opened  clamp  b  is  cautiously 
opened  and  the  piston  of  the  syringe  gently  pressed  so  that 
the  air  slowly  enters  the  burette  to  just  below  the  10  c.c.  mark. 
The  further  steps  are  precisely  as  described  for  atmospheric 
air.  In  this  case,  however,  the  volume  will  be  found  to  have 
become  considerably  reduced  and  the  exact  reading  on  the 
burette  is  noted  and  the  percentage  of  CO2  calculated. 

At  least  three  similarly  collected  samples  of  alveolar  air 
are  to  be  analysed  and  the  results  should  check  to  within 
0.25  per  cent. 

When  all  analyses  have  been  completed  the  burette  is  filled 
with  weak  acid  (0.5  per  cent  H2SO4).  This  is  accomplished  by 
turning  C  into  position  I,  filling  the  burette  with  mercury  and 
the  syringe  with  weak  acid,  inserting  the  nozzle  of  the  syringe 


110  EXPERIMENTAL  PHYSIOLOGY 

at  H  and  then  allowing  it  slowly  to  fill  the  burette.  The  burette 
is  left  filled  with  the  weak  acid. 

Analysis  for  CO2  and  O2. — For  this  purpose,  the  absorp- 
tion part  of  the  apparatus  is  more  complicated  (see  Fig.  32) 
and  is  attached  at  G. 

The  tube  from  the  burette  leads  to  a  three-way  stopcock  J  which  accord- 
ing to  its  position  connects  either  with  D  or  M;  with  the  former  for  the  ab- 
sorption of  CO2  as  described  above  and  with  the  latter  for  the  absorption 
of  O2.  This  part  of  the  apparatus  consists  of  a  spiral  tube  L  ending  below 
in  a  bulb  M  which  is  connected  with  a  reservoir  N.  M  contains  pyrogallic 
acid  dissolved  in  60  per  cent.  KOH  solution  (10  grams  per  100  c.c.)  and  N 
contains  mercury.  These  are  introduced  through  the  side  tube  O  and  the 
levels  are  adjusted  so  that  the  jjieniscus  of  the  pyro  solution  stands  some- 
where on  the  narrow  tube  e  above  the  spiral.  For  convenience  of  filling  and 
cleaning  there  is  a  rubber  joint  at  K  surrounded  by  mercury  so  as  to  prevent 
leaks.  This  is  shown  in  detail  in  the  small  side  sketch  of  Fig.  32.  The  spiral 
is  used  to  increase  the  surface  of  contact  between  gas  and  solution  since 
absorption  of  C>2  is  much  slower  than  that  of  CC>2. 

The  analytical  procedure  is  in  principle  the  same  for  O2  as 
for  CO2  but  it  is  necessary  that  the  tubing  and  connections  be 
filled  with  nitrogen,  instead  of  air,  before  starting  the  analysis. 
This  is  done  by  passing  some  air  back  and  forth  between  the 
burette  and  the  spiral,  until,  on  bringing  the  pyrogallate 
meniscus  to  the  original  mark  on  e,  there  is  no  further  change 
in  the  level  of  the  mercury  in  A.  The  tap  J  is  then  turned  so 
that  g  and  d  communicate,  the  nitrogen  passed  into  D  and 
then  returned  to  A  so  as  to  displace  the  air  entrapped  in  d. 
The  tap  J  is  again  turned  so  that  g  and  e  communicate  and  the 
last  traces  of  O2  removed  from  the  gas  in  the  burette. 

This  preliminary  filling  of  the  apparatus  with  N  is  necessary 
only  when  it  is  used  for  the  first  time  after  assembling;  other- 
wise N  remains  over  in  the  tubing  from  the  previous  analysis. 

In  the  actual  analysis  for  CO2  and  O2,  the  percentage  of 
CO2  is  first  of  all  determined  by  the  procedure  already  described. 
The  tap  J  is  then  turned  so  that  g  and  e  communicate  and  the  O2 
removed,  great  care  being  taken  in  moving  the  air  between 
A  and  L  that  the  pyrogallate  solution  does  not  rise  above  the 
mark  on  e.  The  small  bulb  on  e  serves  to  prevent  this  by 
breaking  up  any  bubbles  that  form.  It  will  be  noticed  that 
as  the  O2  becomes  removed  the  pyro  solution  adhering  to  the 


ALVEOLAR  AIR  111 

walls  of  the  spiral  tube  becomes  much  more  transparent. 
Before  the  final  volume  is  read  in  A,  the  air  entrapped  in  d 
must  be  removed  as  above  described1.  Since  it  takes  some 
time  for  all  O2  to  be  absorbed,  the  final  volume  should  not  be 
read  in  A  until  time  has  been  allowed  for  the  temperature  of 
the  gas  to  come  to  that  of  the  water  in  the  jacket.2 

After  completion  of  the  analysis  the  taps  J  .and  C  are  both 
turned  so  that  the  tubing  is  completely  shut  off. 

Calculation  of  the  percentage  of  Og  is  shown  in  the  example 
on  p.  121. 

The  Tension  of  Carbon  Dioxide  in  Alveolar  Air.— By 
the  gas  laws  each  gas  in  the  alveolar  air,  and  also  the  water 
vapour,  will  exert  a  partial  pressure  or  tension  which  is  equal 
to  that  which  it  would  exert  were  it  alone  present  in  the  space 
occupied  by  the  mixture  of  gases.  This  mixture  consists, 
approximately,  of  5.5  per  cent.  CO2,  16  per  cent,  oxygen, 
79.5  per  cent.  Nitrogen  and  it  is  saturated  with  water  vapour 
at  body  temperature,  37°  C.  Assuming  that  the  barometric 
pressure  is  760  mm.  Hg.,  then,  to  find  the  tension  of  CO2  in 
alveolar  air  we  must  first  of  all  subtract  from  760  the  aqueous 
tension  at  37°  C.  which  equals  48  mm.  Hg.  and  multiply  by 
5.5 
100' 


xSince  absorption  of  C>2  is  relatively  slow,  it  is  advisable  for  routine  work  to 
have  the  reservoir  B  raised  and  lowered  automatically.  The  most  convenient 
way  for  doing  this  is  to  attach  it  by  string  to  one  end  of  a  hinged  metal  rod 
which  rests  on  a  can  placed  on  shafting  that  is  made  to  revolve  at  a  suitable 
rate  by  means  of  a  small  motor. 

2To  correct  for  possible  changes  in  the  temperature  of  the  water  Haldane's 
dummy  tube  is  used.  This  consists  of  a  10  c.c.  tube  in  the  water  jacket,  con- 
nected by  capillary  glass  tubing  with  the  lower  end  of  D.  The  capillary  tubing 
is  furnished  with  a  stop  cock  so  that  it  can  be  opened  to  the  outside.  The  position 
of  this  system  is  shown  on  the  dotted  lines  in  Fig.  32.  At  the  start  of  an  analysis 
the  stop  cock  is  connected  outside  and  the  level  of  the  meniscus  of  NaOH  solution 
marked  on  the  tube  /.  The  stopcock  is  then  turned.  If  this  level  remians  un- 
altered after  the  analysis  there  can  have  been  no  change  of  temperature.  If  it 
has  shifted,  it  is  brought  back  to  the  original  level,  while  g  and  d  are  in  com- 
munication, by  raising  or  lowering  F.  By  this  procedure  the  gas  in  A  is  com- 
pressed or  decompressed  in  proportion  to  the  extent  to  which  it  may  have  ex- 
panded by  heat  or  contracted  by  cold.  Before  taking  the  final  reading  the 
meniscus  in  d  is  of  course  readjusted  by  manipulating  the  screw  clip  a. 


112  EXPERIMENTAL  PHYSIOLOGY. 

Because  of  the  free  diffusibility  of  CO2  through  the  pul- 
monary endothelium,  the  same  tension  must  exist  in  the  blood 
as  in  alveolar  air.  If  the  alveolar  air  be  collected  with  the  least 
possible  disturbance  in  breathing,  this  equilibrium  will  be 
between  the  arterial  blood  leaving  the  lungs  but  if  the  breath 
be  held  it  will  be  between  the  venous  blood  as  it  comes  to 
them.  The  former  value,  i.e.,  the  arterial  tension  of  CO^,  is 
of  very  great  importance  partly  because  it  regulates  the  H-ion 
concentration  of  the  blood  going  to  the  respiratory  and  other 

H2CO3 
centres  (through  the  equation     r  )  an(^  Partly  because  of 


its  specific  action  on  these  centres.  The  most  practical  method 
for  collecting  alveolar  air  without  serious  disturbance  of  breath- 
ing is  that  of  Haldane. 

Experiment  49a.  —  Haldane's  method  for  collecting  alveolar 
air.  —  The  apparatus  consists  of  a  piece  of  wide  bore  rvibber 
tubing  about  1  metre  long  provided  at  one  end  with  a  mouth 
piece,  consisting  of  a  glass  or  brass  tube  of  similar  bore  to  the 
rubber  tubing,  and  somewhat  flattened  at  the  free  end,  with  a 
short  piece  of  narrow-bore  tubing  attached  at  right  angles. 
After  dipping  in  antiseptic  solution  place  the  mouth  piece  in 
the  mouth  of  the  observed  person  and  direct  him  to  close  the 
lips  tightly  round  it,  and  to  continue  breathing,  by  inspiring 
through  the  nose  and  expiring  through  the  tube  for  a  minute  or 
two  so  that  the  person  may  become  accustomed  to  the  pro- 
cedure. Meanwhile  attach  a  clean  all-glass  10  c.c.  syringe  with 
the  piston  lightly  smeared  with  vaseline  (if  there  is  too  much 
vaseline  it  will  absorb  an  appreciable  amount  of  CO2)  to  the 
side  tube  by  means  of  a  short  piece  of  rubber  tubing.  Now 
instruct  the  person  to  make  a  forced  expiration  (really  to  blow 
out)  through  the  tube  for  a  period  of  time  equal  to  that  of  an 
ordinary  expiration  and  to  close  the  opening  of  the  tube  in  the 
mouth  with  the  tongue  when  he  has  completed  the  expiration' 
Immediately  he  has  done  this,  withdraw  the  piston  of  the 
syringe  (not  too  hurriedly  so  as  to  avoid  breaking  the  syringe) 
and  when  a  little  over  10  c.c.  of  air  has  been  collected  ins.truct 
the  person  to  continue  breathing  through  the  tube  as  before. 


ALVEOLAR  AIR.  113 

This  sample  of  alveolar  air  is  discarded  by  being  pressed  back 
into  the  breathing  tube,  the  object  of  its  collection  being  to 
have  the  side  tube  and  nozzle  of  the  syringe  filled  with  alveolar 
air  (instead  of  outside  air)  when  the  main  sample  is  taken. 
After  several  normal  breaths  have  again  been  taken  through 
the  tube,  collect  another  sample  (of  over  10  c.c.)  of  alveolar 
air  and  remove  the  syringe  meanwhile  closing  its  opening 
by  the  finger,  and  analyse  in  the  gas  burette. 

The  forced  expiration  from  which  the  above  sample  of 
alveolar  air  was  taken  followed  a  normal  inspiration  but  it  is 
clear  that  the  percentage  of  CO2  which  it  contains  will  be  less 
than  that  in  a  forced  expiration  made  immediately  after  a 
normal  expiration.  To  find  the  average  percentage  of  CO2  in 
the  alveolar  air  it  is  therefore  necessary  to  collect  another 
sample  taken  from  a  forced  expiration  following  a  normal 
expiration.  This  is  a  more  difficult  procedure  since  the  person 
must  blow  out  after  a  normal  expiration  for  a  period  of  time 
equal  to  that  of  the  normal  expiration.  With  a  little  practice 
it  can,  however,  be  satisfactorily  accomplished.  Collect  and 
analyse  for  CO2  at  least  two  samples  of  alveolar  air  following 
inspiration  and  expiration.  If  the  results  do  not  check  to 
within  0.2  per  cent,  repeat  the  observations  until  they  do. 
Calculate  the  average  tension  of  CO2  in  the  alveolar  air.  The 
chief  source  of  error  in  the  above  method  depends  on  the  fact 
that  the  percentage  of  CO2  will  progressively  increase  in  each 
succeeding  portion  of  the  air  of  the  forced  expiration,  because 
a  constant  amount  of  CO2  is  being  discharged  from  the  blood 
into  a  diminishing  volume  of  alveolar  air.  It  is  for  this  reason 
that  great  care  must  be  taken  to  have  the  forced  expiration 
of  the  same  duration  as  a  normal  one. 

Determination  of  the  percentage  of  CO2  which  is  in  equi- 
librium with  the  tension  of  CO2  in  the  venous  blood  of  the  lungs 
is  much  more  difficult.  To  do  it  with  any  degree  of  accuracy 
it  is  necessary  to  determine  the  percentage  of  CO2  in  a  series 
of  fractions  of  a  deep  expiration  which  immediately  follows 
upon  a  deep  inspiration  from  a  gasometer,  or  rubber  bag,  con- 
taining air  with  about  10  per  cent,  of  CO2.  The  CO2  decreases 
steadily  in  each  succeeding  fraction  until  a  level  is  reached 


EXPERIMENTAL  PHYSIOLOGY 

which  represents  the  percentage  of  this  gas  which  is  in  equi- 
librium with  its  tension  in  the  pulmonary  venous  blood. 

A  rough  approximate  idea  of  the  venous  tension  of  CO2  can 
be  obtained  by  determination  of  its  percentage  in  the  alveolar 
air  at  the  breaking  point,  which  means  the  point  beyond  which 

. J:he  breath  can  no  longer  be  held. 

Experiment  49b.~ After  a  normal  inspiration  hold  the  breath 
as  long  as  possible,  then  make  a  forced  expiration  through  a 
Haldane  tube  and  collect  a  sample  of  the  air  for  analysis  of 
COj  (two  if  possible).  Repeat  this  experiment  after  taking  a 
deep  inspiration  immediately  before  holding  the  breath.  Keep 
a  precise  record  of  the  time  during ^which  the  breath  was  held, 
in  both  observations.  Count  the  pulse  and  examine  for  cya- 
nosis during  the  time  the  breath  is  held.  The  percentage  of 
CO2  in  alveolar  air  at  the  breaking  point  is  considerably  above 
the  CO2  tension  of  the  normal  venous  blood  because  the  blood 
has  completed  the  circuit  of  the  circulation  several  times  during 
the  time  the  breath  was  held.  Each  time  the  blood  returns 
to  the  lungs  it  of  course  carries  more  and  more  CO2  which 
raises  the  tension  of  this  gas. 

The  breaking  point  experiment  really  tells  us  the  tension 
of  CO2  in  arterial  blood  beyond  which  the  activities  of  the 
respiratory  centre  can  no  longer  be  inhibited  by  voluntary 
effort.  This  tension  will  not  always  be  the  same  because  it 
will  depend  on  whether  or  not  other  chemical  changes  are 
occurring  in  the  blood  that  are  capable  of  affecting  the  excita- 
bility of  the  centre.  One  such  change  is  the  O2  tension  of  the 
blood.  When  this  becomes  depressed  below  a  certain  level  the 
respiratory  centre  is  stimulated  and  it  is  consequently  to  be  ex- 
pected that  part  of  the  stimulus  at  the  breaking  point  is  due 
to  this  cause.  That  this  is  the  case  can  be  shown  by  repeating 
the  breaking  point  experiment  after  filling  the  lungs  with 
oxygen. 

Experiment  49c.— Take  a  deep  inspiration  from  a  rubber  bag  or 
spirometer  containing  oxygen,  then  hold  the  breath  to  the 
breaking  point  and  analyse  a  specimen  of  alveolar  air  for  CO2 
(and  for  O2  if  possible).  Keep  a  record  of  the  time  during 
which  the  breath  was  held. 


ALVEOLAR  AIR.  115 

The  higher  tension  of  O2  still  remaining  in  the  arterial  blood 
at  the  breaking  point  is  not  the  only  cause  for  the  decidedly 
longer  time  during  which  the  breath  can  be  held  in  the  foregoing 
experiment,  another  cause  being  that  the  CO2-combining  power 
of  the  blood  will  be  less  because  it  contains  relatively  more 
oxy haemoglobin,  than  in  the  first  experiment.  Oxyhaemo- 
globin  is  more  acid  than  reduced  haemoglobin. 

In  both  of  the  above  experiments  examine  the  gums  and 
the  base  of  the  finger  nails  for  evidence  of  cyanosis  (blueness) 
and  note  the  exact  time  at  which  it  appears. 

The  Effects  of  Forced  Breathing.— When  the  breathing 
is  made  as  deeply  as  possible,  without  materially  altering  the 
rate,  the  alveoli  become  excessively  ventilated  with  the  result 
that  the  CO2  tension  falls  far  below  the  normal  level  and  free 
CO2  diffuses  from  the  blood.  The  free  CO2  of  the  blood  is 
'washed  out'  or  'blown  off'  with  the  consequence  that  the  acid- 
base  equilibrium  of  the  blood  changes,  leaving  a  relative  excess 
of  base.  The  condition  of  alkalosis  hereby  established  causes 
alteration  in  various  physiological  functions  and  the  following 
experiments  are  designed  to  demonstrate  these. 

Experiment  49d. — Have  a  person,  while  sitting,  respire  as  deeply 
as  possible,  at  the  normal  rate,  for  ten  minutes.  During  this 
time  count  the  pulse  and  measure  the  systolic  blood  pressure. 
Examine  also  for  evidence  of  cyanosis.  After  the  forced  breath- 
ing, it  will  be  found  that  for  a  time  the  person  does  not  volun- 
tarily breathe — apnoea.  Observe  the  thorax  very  carefully  to 
note  the  time  at  which  the  first  indication  of  breathing  returns. 
Note  the  character  of  the  first  breath  and  of  those  which 
succeed  it.  Make  a  diagram  showing  the  character  of  the 
breathing;  also,  count  the  pulse  as  frequently  as  possible  and 
look  carefully  for  cyanosis. 

Experiment  49e.—  Measure  the  percentage  of  CO2  in  the  alveolar 
air  of  a  person  then  instruct  him  to  breathe  deeply  for  ten 
minutes  (as  in  Experiment  43d),  and  during  the  last  expiration 
take  another  sample  of  alveolar  air.  Take  a  third  sample  at 
the  time  the  breathing  just  returns  and  a  fourth  one  when  the 
normal  breathing  is  reestablished  (it  will  be  advisable  to  have 
at  least  two  sampling  syringes  for  these  purposes).  Chart  the 


116  EXPERIMENTAL  PHYSIOLOGY 

results  of  the  analysis  along  with  a  diagrammatic  curve  of  the 
breathing.  It  will  be  found  that  the  CO2  tension  is  greatly 
lowered  by  the  forced  breathing  (what  is  the  reason?)  and  that 
normal  breathing  returns  at  a  tension  which  is  decidedly  below 
the  normal.  How  do  you  explain  this  result? 

Repeat  this  experiment  with  the  difference  that  the  last  of  the 
deep  inspirations  is  taken  from  a  rubber  bag  containing  oxygen. 
Note  the  duration  of  the  apnoea,  the  occurrence  of  cyanosis 
and  the  alveolar  CO2  tension  at  the  return  of  breathing.  Ex- 
plain the  cause  for  any  changes  from  the  previous  results. 

When  the  forced  breathing  is  kept  up  for  some  time,  marked 
changes  occur  in  the  acid  base  equilibrium  of  the  blood  because 
of  the  blowing  off  of  CO2.  A  condition  of  alkalosis  results  and 
the  kidneys  respond  by  excreting  urine  with  relatively  less 
acid  than  normal.  The  alkalosis  also  causes  various  symptoms 
the  most  striking  of  which  affect  the  nervous  system. 
Experiment  49f . — Measure  the  alveolar  CO2  and  the  total  acidity 
of  the  urine  of  a  person  who  has  not  recently  performed  the 
forced  breathing  experiment.  For  the  latter  purpose,  shake 
about  15  c.c.  of  urine  with  about  0.5  gm.  of  a  soluble  oxalate, 
filter,  and  titrate  10  c.c.  of  the  nitrate  against  0.05  N  NaOH 
using  phenolphthalein  as  indicator.  Also  test  the  knee  jerks 
(p.  105).  Have  this  person  breathe  deeply  for  half  an  hour, 
unless  the  process  causes  great  discomfort  when  it  should  be 
terminated  earlier.  At  frequent  intervals  observe  the  pulse, 
test  the  knee  jerks,  look  for  evidence  of  venous  congestion 
(cyanosis)  and  test  the  excitability  of  the  seventh  nerve  by 
tapping  with  the  finger  at  the  point  of  its  emergence  from  the 
skull.  In  a  normal  person  this  does  not  cause  any  twitching 
of  the  face  muscles  but  as  alkalosis  developes  such  occurs  and 
becomes  progressively  more  marked.  (Chvosek's  sign  for 
tetany).  Also  examine  carefully  for  the  appearance  of  tonic 
contractions  of  the  flexor  and  adductor  muscles  of  the  hand  and 
forearm.  Towards  the  end  of  the  period  of  forced  breathing 
this  other  symptom  of  tetany  will  often  be  quite  evident  but 
if  not  so  it  can  be  made  to  develop  by  constricting  the  arm  by 
means  of  a  blood  pressure  cuff,  or  a  rubber  band.  (Trousseau's 
sign  for  tetany).  After  discontinuance  of  the  forced  breathing 


ALVEOLAR  AIR  117 

observe  the  duration  of  the  apnoea  (and  compare  with  that 
following  less  prolonged  hyperpnoea) ,  and  the  manner  of  return  of 
normal  breathing,  look  also  for  evidence  of  cyanosis.  Measure 
the  alveolar  CC>2  when  breathing  returns.  Determine  for  how 
long  hyperexcitability  of  the  motor  neurones  is  evident.  When 
normal  conditions  become  reestablished  make  a  record  of 
the  subjective  symptoms  (the  sensations  experienced  by  the 
observed  person).  Find  out  whether  any  visual,  auditory  or 
peripheral  skin  sensations  (numbness,  tingling,  etc.)  were 
experienced.  Finally  collect  another  specimen  of  urine  and 
determine  its  total  acidity. 


CHAPTER   XIII. 

RESPIRATORY  EXCHANGE  IN  MAN.     (TISSOT- 
CARPENTER  METHOD).* 

The  principle  of  the  method   consists  in   the  collection  of  a 
definite  volume  of  expired  air  in  an  accurate  spirometer  and  the 
subsequent  analysis  of  a  mixed  sample  of  it.     It  is  then  possible  to 
compute  the  energy  metabolism   (Indirect  Calorimetry).       After 
correcting  for  temperature  and  pressure,  the  total  CO2  output  and 
O2  intake,  and  from  them  R.Q.,  are  then  computed. 
Experiment  50. — -The  subject  sits  on  a  chair  and  takes  the  mouth- 
piece A  (Fig.  33)  of  the  respiration  tube  in  his  mouth.     The 
mouth-piece  consists  of  an  elliptical  rubber  flange  with  a  hole 
in  the  centre  connected  with  the  respiration  tube.     Two  rubber 
lugs  are  provided  and  these  are  gripped  between  the  teeth,  the 
flange  being  placed  between  the  lips  and  the  gums.     The  nose 
is  tightly  closed  by  a  suitable  clamp. 

The  RESPIRATION  TUBE  leads  to  the  valves,  B,  (Douglas'  or  Pearce's),  the 
end  of  the  expiration  tube  of  which  leads  to  a  large  stopcock,  C,  connected 
with  the  interior  of  the  spirometer.  The  latter  consists  of  a  100-litre  inverted 
aluminium  cylinder,  D,  suspended  from  a  pulley,  E,  in  a  water  bath  between 
the  double  walls  of  an  upright  stationary  cylinder,  F.  As  the  aluminium 
cylinder  rises  out  of  the  water  on  account  of  air  entering  it,  its  weight  be- 
comes greater.  To  allow  for  this,  the  wheel  is  made  excentric,  (G),  so  that 
as  E  revolves,  with  elevation  of  the  spirometer,  a  weight  connected  by  a 
thread  to  the  circumference  of  the  excentric  exercises  a  progressively  greater 
pull  on  the  spirometer,  and  so  exactly  counterpoises  it.  The  top  of  the 
cylinder  is  provided  with  holes  for  the  insertion  of  a  thermometer  and  of  a 
tube  and  stopcock  for  drawing  off  the  sample  of  air  for  analysis. 

*Since  the  main  thing  to  be  learned  in  this  observation,  apart  from  the  methods 
of  analysis  of  the  air,  is  the  method  of  calculation  of  the  respiratory  quotient 
and  of  the  total  respiratory  exchange,  the  experiment  can  be  profitably  assigned 
to  a  larger  group  of  students  than  the  usual.  After  the  sample  of  air  has  been 
collected,  certain  members  of  the  group  will  proceed  to  analyse  it  and  make  the 
necessary  calculations.  Since  the  greatest  cause  for  delay  in  this  experiment  is  in 
the  analysis  of  the  oxygen  in  the  air  sample,  this  procedure  should  be  practised 
before  starting  the  experiment,  and  a  student  who  has  already  had  experience 
with  the  gas  burettes  should  demonstrate  the  technique  to  others. 

118 


RESPIRATORY  EXCHANGE. 


119 


FIG.  33.  Tissot-Carpenter  Spirometer,  Douglas  mouthpiece  and  Pearce's  valves.  The  dotted 
lines  in  the  diagram  indicate  the  outline  of  the  aluminium  cylinder  while  in  the  water  seal  between 
the  outer  and  inner  steel  cylinders,  the  position  of  the  latter  of  which  is  also  indicated  by  dotted 
lines.  For  further  references  see  context.  The  inserts  show  the  Douglas  mouthpiece  and  Pearce 
valves,  the  latter  of  which  is  made  as  follows:  Prepared  casings  used  in  the  manufacture  of 
bologna  sausage  are  obtained  preserved  in  salt,  and  they  will  keep  indefinitely  on  ice.  When 
needed  a  short  piece  is  taken,  washed  free  from  salt  by  allowing  water  from  the  tap  to  run  through  it, 
and  softened  in  a  weak  glycerine  solution.  The  gut  becomes  very  soft  and  pliable,  and  does  not  dry 
quickly.  A  piece  of  the  casing  about  10  cm.  long  is  threaded  through  a  glass  tube  of  about  15  mm. 
bore  and  4  to  6  cm.  long.  One  end  of  the  casing  is  brought  around  the  outside  of  the  tubing  and 
secured  by  means  of  a  thread.  The  lower  end  of  the  membrane  is  pinched  off  and  the  casing  is  then 
cut  a  little  more  than  half  way  across  its  middle,  so  that  the  opening  will  lie  just  within  the  free  end 
of  the  tube  when  the  casing  is  drawn  back  through  it.  The  loose  end  of  the  casing  is  slightly 
twisted — an  essential  procedure — and  is  then  secured  by  a  thread  on  the  outer  side  of  the  tube. 


120  EXPERIMENTAL  PHYSIOLOGY. 

In  conducting  the  observation,  the  spirometer  is  first  set  at  zero 
on  the  scale  at  the  side.  The  subject  then  breathes  for  some  time 
through  the  valves  and  a  side  tube  with  the  stopcock  turned  off. 
When  the  breathing  is  comfortable,  the  stopcock  is  turned  so  that 
the  air  enters  the  spirometer,  and  the  side  tube  is  closed  by  placing 
a  clamp  on  the  rubber  tubing  on  its  free  end,  the  exact  moment 
being  noted.  The  air  is  allowed  to  collect  for  a  definite  period  of 
time  (4  to  5  minutes  for  a  subject  at  rest),  at  the  end  of  which  the 
stopcock  is  again  turned  and  the  side  tube  opened  so  as  to  connect 
with  the  outside.  The  temperature  in  the  spirometer  and  the 
barometric  pressure  are  then  carefully  noted,  as  well  as  the  volume 
of  air  in  the  spirometer.  The  number  of  respirations  during  the 
observation  is  also  counted. 

The  sample  of  air  for  analysis  is  collected  in  an  all-glass  syringe, 
the  nozzle  of  which  fits  into  the  rubber  tubing  of  the  stopcock  on 
the  top  of  the  cylinder.  To  allow  for  the  dead  space  of  the  tubing, 
the  syringe,. after  filling,  is  removed  from  the  tubing  (after  turning 
off  the  tap  again),  emptied  and  reconnected.  The  piston  is  then 
moved  out  and  in  several  times,  and  the  syringe,  filled  with  air,  is 
removed  to  the  gas  analysis  burette  and  the  analysis  made  according 
to  the  directions  in  Exp.  49. 

It  is  particularly  important  to  make  certain  that  all  the  oxygen 
is  absorbed  by  the  pyrogallate  and  that  the  air  entrapped  in  the 
tubing  leading  to  the  CCVabsorption  pipette  is  included  in  the 
analysis. 

THE  CALCULATIONS. — The  following  have  to  be  determined: 

1.  Per  cent  CO2  and  O2. 

2.  Respiratory  Quotient. 

3.  Total  vol.  CO2  and  O2  respired  per  kgm.  body  weight  and  per  square 
metre  of  body  surface. 

4.  Calorie  expenditure  (indirect  calorimetry). 

The  following  report  form  should  be  filled  in  as  indicated,  the  necessary  calcu- 
lations being  made  by  use  of  the  tables  in  the  appendix. 

METABOLISM  SHEET. 

Name  Age  Wt.  Ht. 

Surface  area  calculated  =  (Du  Bois  method). 

Corrected  Volume  of  Respired  Air. 

(1)  Total  volume  of  air  respired  in  15  min.  =  100  Litres. 

(2)  Actual  Temp.  =  20°  C. 


RESPIRATORY  EXCHANGE.  121 

(3)  Actual  Bar.  Press.  =  747  mm.  Hg. 

(4)  Corrected   Bar.    Press.    ((3)    -Factor  in   Table  III)  =747-  (17.4+2.41)  = 

727.19  mm.  Hg. 

(5)  Volume  of  Resp.  Air  at  760  mm.  and  0°  C.  (  (1)  X  Factor  in  Table  IV)  100  X 
0.89062=89.062  Litres. 

(6)  Corrected  Volume  of  Resp.  Air 

(a)  per  mii1ute=  5.  937  Litres. 
(6)  per  hour  =  356.248  Litres. 

Calculations  of  02  A  bsorbed  and  COi  Eliminated. 

(7)  Volume  per  cent.  CO2  in  spirometer  air  =4.0. 

(8)  Volume  per  cent.  O2  in  spirometer  air  =  16.  5. 

(9)  Volume  per  cent.  CO2  and  O2  in  spirometer  air  (7)  (8)  =20.5. 

(10)  Volume  per  cent.  N  in  spirometer  air  (100)  -  (9)  =79.5. 

(11)  Volume  per  cent.  N  in  room  air  taken  as  79  =  79.0. 

(12)  Oxygen  equivalent  of  (10)  =  (10X0.265)  =79.5X0.265  =21.06. 

(This  may  also  be  obtained  from  Table  I). 

(13)  Volume  per  cent.  O2  absorbed  (12)  -  (8)  =21.06-16.5  =  4.56. 

(14)  Volume  percent.  CO2  eliminated  (7)  -(.03)  =4.0-0.03  =  3.97. 

(15)  Total   O2  volume    (standard   conditions)    absorbed   per   hr.    (13)X6(b)  = 

16.24  Litres. 

(16)  Total  CO2  volume  (standard  conditions)  eliminated  per  hr.  (14)X6(b)  = 

14.14  Litres. 


The  Caloric  Value  Calculated  from  the  Gas  Exchange. 

(Indirect  Calorimetry). 

This  can  be  done  by  using  table  V  (Appendix)  provided  we  know  the  non- 
protein  R.Q,  which  is  given  in  the  1st  column  of  the  table.  This  latter  is  obtained 
by  deducting  from  the  total  CO2  eliminated,  the  CO2  derived  from  protein  (found 
by  multiplying  the  urinary  N  by  9.35)  and  by  deducting  from  the  total  O2  ab- 
sorbed, the  O2  required  to  oxidise  protein  (found  by  multiplying  urinary  N  by 
8.45).  Suppose  for  example,  that  14.4  gm.  N  is  excreted  in  the  24  hrs.  urine; 
i.e.,  0.6  gm.  per  hr.  then,  9.35  X0.6  =  5.610  gm.  CO2  or  (since  1  gm.  CO2  =  0.5087  1) 
2.85  1  must  be  subtracted  from  14.14  Litres  giving  11.29  Litres,  and  similarly 
8.45  X.  6  =  5.070  gm.  O2  or  (since  1  gm.  O2  =  0.7  1)  3.5490  must  be  subtracted 

from  16.24  giving  12.69.     The  non-protein   R.Q.  is  therefore  -        -    =0.889. 

1  —  .  *  K  ' 

Referring  to  table  V  we  see  that  at  R.Q  0.889  1  litre  of  O2  equals  4.91  C.  .'.  in 
Ihr.  4.91X16.24  =  79.73C  were  expended.  As  a  matter  of  fact  for  many  pur- 
poses it  is  sufficiently  accurate  to  use  the  uncorrected  R.Q.  for  table  V. 


CHAPTER    XIV. 

DETERMINATION  OF  THE  GASES  OF   BLOOD  BY  THE 
PUMP  METHOD. 

When  blood  is  repeatedly  exposed  to  a  vacuum  all  of  its  gases  are 
evolved.  The  evolved  gases  can  then  be  transferred  to  a  suitable 
burette  and  their  nature  and  relative  amounts  determined.  The 
gas  cannot  be  completely  removed  by  one  exposure  of  the  blood 
in  a  vacuum,  because  in  such  a  case  the  gas  would  be  evolved  only 
until  equilibrium  had  become  established  between  the  partial 
pressure  produced  by  the  evolved  gas,  and  that  still  present  in 
the  blood.  It  is  necessary  to  repeat  the  evacuation  several  times. 
For  this  purpose  a  mercury  pump  is  usually  employed,  but  satis- 
factory evacuation  can  also  be  brought  about  by  using  the  simpler 
apparatus  described  in  the  following  experiment. 

Experiment  51. — Place  about  15  c.c.  defibrinated  ox  blood  in 
a  500  c.c.  flask,  and  fill  the  latter  with  alveolar  air  by  expiring 
deeply  into  it  through  a  piece  of  wide-bore  rubber  tubing,  or  better, 
through  a  glass  tube  which  is  connected  in  its  course  with  a  bottle 
filled  with  glass  beads.  This  condenses  and  removes  the  water  from 
the  air.  Rotate  the  flask,  so  that  the  blood  forms  a  thin  film  on  the 
walls,  but  do  not  shake  in  such  a  manner  as  to  cause  the  blood  to 
froth.  While  rotating,  occasionally  expire  through  the  tube  into 
the  flask  so  as  to  maintain  the  percentage  of  carbon  dioxide  con- 
stant. Continue  this  procedure  for  about  three  minutes,  and  then 
close  the  flask.  By  this  means  the  blood  absorbs  oxygen  to  full 
saturation,  and  carbon  dioxide  to  the  same  extent  as  the  blood  in 
the  pulmonary  capillaries. 

Meanwhile  the  bulb  of  the  blood  receiver  (Fig.  34A)  is  partially 
evacuated  by  connecting  it,  by  means  of  the  attached  piece  of 
rubber  tubing,  to  a  (water)  vacuum  pump.  The  screw  clip  (1)  is 
then  tightened  (leaving  as  long  a  piece  of  tubing  beyond  the  clip 

122 


BLOOD  GASES. 


123 


as  possible),  the  side  tube  of  the  pump  opened*  and  the  blood  bulb 
removed.  A  few  drops  of  the  anti-foaming  solution  (caprylic 
alcohol  or  isoamylisovalerate),  is  placed  in  the  receiver.  This  is 


FIG.  34.     Apparatus  for  measurement  of  gases  of  blood  by  pump  method.       For 
description,  see  Context. 


*The  water  must  never  be  turned  off  from  the  pump  while  this  is  connected 
with  a  partially  or  completely  evacuated  vessel.  Always  allow  air  into  the  pump 
before  turning  off  the  water. 


124  EXPERIMENTAL  PHYSIOLOGY. 

accomplished  by  taking  about  0.5  c.c.  of  the  fluid  in  a  glass  tube 
of  sufficient  external  diameter  to  fit  tightly  the  rubber  tubing  of 
the  receiver  (a  1  c.c.  pipette  with  the  delivery  end  partially  cut 
off).  Before  inserting  the  pipette  into  the  rubber  tubing,  the  lumen 
of  the  latter  beyond  the  clip  is  filled  with  the  anti-foaming  solution, 
so  that  no  air  may  enter  the  receiver,  and  after  inserting,  the  screw 
clip  (1)  is  very  cautiously  opened  and  about  0.1-0.2  c.c.  of  the  solu- 
tion allowed  to  run  in,  after  which  the  clip  is  again  screwed  tight, 
the  pipette  removed,  and  the  solution  still  in  it  replaced  in  the 
stock  bottle.  The  receiver  is  reattached  to  the  water  pump  and 
evacuated  as  far  as  possible. 

It  is  then  attached  to  tube  D  of  the  blood  pump  and  evacuation 
completed  by  manipulating  the  pump  as  described  below  for  the 
evacuation  of  blood.  When  completely  evacuated,  as  judged  by 
the  inability  to  suck  over  more  air,  screw  clip  1  is  closed  and  the 
blood  receiver  removed  from  the  pump. 

Ten  c.c.  of  blood  is  now  placed  in  the  receiver.  To  accomplish 
this,  blood  is  removed  from  the  flask  by  means  of  the  special  10  c.c. 
pipette,  using  only  gentle  suction  and  filling  to  the  upper  mark. 
All  air  is  squeezed  out  of  the  tubing  on  the  blood  bulb,  and  the 
end  of  the  pipette  inserted  in  the  tubing,  being  careful  to  see  that 
no  air  bubbles  are  present  at  the  union.  Holding  the  pipette  and 
blood  bulb  vertically,  the  clip  is  very  cautiously  unscrewed,  and 
the  blood  allowed  to  flow  from  the  pipette  into  the  bulb  until  the 
lower  mark  on  the  former  is  reached.  The  capacity  between  the 
two  marks  is  10  c.c.  After  tightening  the  screw  clip,  the  pipette  is 
removed  and  the  blood  left  in  the  tubing  is  squeezed  out. 

The  blood  pump  must  now  be  prepared. 

This  consists  of  a  50  c.c.  all-glass  (Luer)  syringe  (B),  with  vaseline  between  the 
walls  and  piston,  the  nozzle  being  connected  by  thick-walled  rubber  tubing,  /, 
with  the  single  tube  of  a  three-way  stopcock  (C).  Of  the  other  tubes  of  the 
stopcock,  one  (D)  runs  to  connect,  by  narrow-bore  glass  tubing,  with  the  blood 
bulb  and  the  other  (£)  to  the  gas  burette  (F) — a  10  c.c.  graduated  pipette  is  satis- 
factory. To  avoid  all  risk  of  air  leakage  into  the  syringe,  this  is  manipulated  in  an 
o  1-bath  (O)  as  shown  in  the  figure.  The  barrel  of  the  syringe  is  clasped  at  its 
upper  end  by  a  brass  collar  (L)  which  is  held  by  the  iron  rod  (R)  to  the  upright 
(£/).  To  the  latter  is  also  hinged  the  free  ends  of  another  iron  rod  bent  on  itself 
(S),  the  bend  being  about  30  cm.  from  the  free  ends.  Two  strips  of  brass  are 
loosely  attached  to  the  two  arms  of  the  bent  rod  on  either  side  of  the  syringe 
where  they  cross  it,  and  these  run  down  to  connect  with  the  head  of  the  piston  of  the 


BLOOD  GASES.  125 

syringe.  This  connection  will  vary  with  the  exact  shape  of  the  head  of  the  piston,  but 
in  any  case,  free  play  must  be  possible  at  the  joint.  In  the  syringe  used  in  this 
laboratory  the  head  of  the  piston  is  ring  shaped  and  is  satisfactorily  connected 
by  fitting  a  wooden  bobbin  in  the  ring  and  attaching  the  brass  strips  to  the  end 
of  the  bobbin.  The  syringe  is  surrounded  by  a  glass  cylinder  containing  a  fairly 
heavy  mineral  oil  (Mobile  oil)  and  this  cylinder  is  attached  to  the  iron  lever  so 
that  it  moves  up  and  down  with  the  piston. 

The  first  step  in  preparing  the  blood  pump  is  to  get  rid  of  all 
the  dead  space  in  the  tubing  and  connections.  This  is  readily 
accomplished,  for  E,  by  turning  stopcock  C  so  that  E  communicates 
with  B,  raising  the  levelling  burette  (G),  and  simultaneously  with- 
drawing the  piston  of  the  syringe  by  depressing  the  lever  until 
about  20  mm.  of  mercury  has  collected  on  the  top  of  the  piston. 
The  stopcock  is  then  turned  so  that  B  and  D  are  connected  and 
the  piston  raised  until  all  the  air  is  expelled  and  mercury  completely 
fills  tube  D.  Any  drops  of  mercury  falling  from  the  open  end  of  D 
must  be  caught  in  a  small  beaker.  The  mercury  left  on  the  top  of 
the  piston  seals  this  completely  during  the  subsequent  manipula- 
tions. 

After  squeezing  all  air  out  of  the  tubing  on  the  blood  receiver, 
this  is  connected  with  D,  and  immersed  in  a  jug  containing  water 
at  45°  C.  Having  turned  C  so  that  B  communicates  with  D,  the 
piston  is  then  depressed  to  about  the  20  c.c.  mark,  and  while  still 
depressed  the  screw  clip  (1)  is  opened.  About  this  time  the  blood 
will  begin  to  "boil"  and  the  gases  given  off  from  it  will  pass  into 
the  vacuum  above  the  mercury  in  the  syringe.  C  is  turned  so  that 
B  is  closed  off  and  the  piston  allowed  slowly  to  ascend.  (It  must 
not  be  allowed  to  ascend  too  rapidly,  since  this  might  break  the 
syringe).  The  gas  which  has  collected  in  the  syringe  is  then  ex- 
pelled into  the  burette  (F)  by  turning  C  so  that  B  and  E  communi- 
cate and  pressing  up  the  piston.  After  all  the  gas  is  out  of  the 
syringe,  the  mercury  is  allowed  to  run  into  E  a  short  distance, 
being  careful  not  to  allow  any  to  get  into  F.  This  first  process 
obviously  removes  only  a  small  fraction  of  the  total  gas  in  the  blood, 
and  it  must  be  repeated  several  times  exactly  as  described  above, 
until  no  more  gas  can  be  secured.  The  dislodgement  of  the  gas 
from  the  blood  is  greatly  accelerated  by  warmth  and  by  occasionally 
removing  the  bulb  from  the  water-bath  and  shaking  briskly. 

It  is  now  necessary  to  measure  and  analyse  the  evolved  gas. 


126  EXPERIMENTAL  PHYSIOLOGY. 

For  this  purpose  the  piston  is  cautiously  pushed  up,  with  E  and  B 
in  communication,  until  mercury  stands  at  the  zero  mark  on  the 
neck  of  the  gas  burette.  The  clip  (4)  is  then  screwed  down  and 
the  levelling  burette  (G)  lowered  until  the  menisci  stand  at  the 
same  level  in  it  and  the  burette.  This  brings  the  gas  to  atmospheric 
pressure  and  the  volume  is  read  and  noted.  The  reading  gives  the 
C.C.  of  gas  in  10  c.c.  blood.  The  volume  should  be  reduced  to 
standard  temperature  and  pressure  (for  calculation  see  Exp.  50). 
To  analyze  the  gas  a  40  per  cent,  solution  of  sodium  hydroxide  is 
sucked  from  a  watch  glass  into  a  2  c.c.  all-glass  syringe,  and  the 
tube  of  the  syringe  inserted  in  the  side  tube  (H).  All  air  must  be 
expelled  from  this  tube.  With  the  pinchcock  (6)  closed,  the  clip 
(5)  is  opened,  while  gentle  pressure  is  being  maintained  on  the 
piston  of  the  small  syringe  so  that  the  mercury  may  not  run  into 
it.  The  NaOH  runs  up  to  the  top  of  the  mercury  column  (F),  and 
when  it  is  all  in,  clip  5  is  again  screwed  down.  The  syringe  (I)  is 
removed  and  F  inverted  several  times  so  that  the  carbon  dioxide 
in  the  gas  contained  in  it  may  be  thoroughly  absorbed.  On  now 
opening  clip  6,  the  mercury  will  rise  in  F,  and  by  adjusting  the 
levelling  tube  the  shrinkage  in  volume  due  to  the  absorption  of 
CC>2  can  be  ascertained  and  the  percentage  of  this  gas  determined. 
The  reading  is  taken  which  corresponds  to  the  top  of  the  NaOH 
solution,  a  similar  amount  of  NaOH  solution  being  placed  on  the 
*.op  of  the  mercury  in  the  levelling  tube.  Care  must  be  taken  to 
see  that  all  the  CO2  is  absorbed. 

To  absorb  the  oxygen,  about  a  gram  of  pyrogallic  acid  is  dis- 
solved in  2  c.c.  of  water  in  the  watch  glass,  the  solution  is  introduced 
into  jP.  and  the  further  manipulations  conducted  in  the  same 
manner  as  for  the  NaOH  solution.  The  gas  which  remains  when 
both  CO2  and  O2  are  absorbed  is  nitrogen.  There  should  not  be 
more  than  0.1-0.2  c.c.,  any  larger  amount  being  due  to  air  leakage 
into  the  apparatus  during  the  manipulations.*  By  taking  proper 
precautions,  however,  the  residual  nitrogen  should  never  be  more 
than  0.3-0.5  c.c.  The  results  are  to  be  calculated  to  give  the  amounts 
of  each  gas  in  100  c.c.  of  blood. 

*If  any  considerable  amount  of  nitrogen  is  left,  its  volume  should  be  measured, 
and  after  subtracting  C>2,  the  volume  of  C>2  that  must  have  been  introduced,  as 
air,  calculated  and  subtracted  from  the  actually  observed  O2. 


BLOOD  GASES.  127 

When  the  analysis  is  completed,  the  mercury  is  run  out  from  the 
burette  by  the  side  tube  (H),  after  removing  the  stopcock  (C), 
and  the  burette  thoroughly  washed  with  water.  The  mercury  and 
alkali  pyrogallate  solution  (which  is  now  brown  in  colour)  are  then 
washed  in  running  water  until  the  washings  react  neutral  to  litmus 
paper.  The  mercury  should  then  be  transferred  to  a  separating 
funnel  containing  a  dilute  solution  of  sulphuric  acid.  The  blood 
bulb  should  also  be  cleaned  immediately,  since  otherwise  a  sticky 
precipitate  which  is  difficult  to  remove  adheres  to  the  walls. 


CHAPTER   XV. 

DETERMINATION  OF  BLOOD  GASES  BY  THE 
CHEMICAL  METHOD 

Instead  of  pumping  the  gases  out  of  blood,  they  may  be  dis- 
placed by  chemical  means.  Each  method  has  its  own  advantages. 
By  the  pump  the  gases  are  obtained  unmixed  with  air  so  that  their 
analysis  tells  us  directly  how  much  of  each  is  contained  in  the  blood. 
By  the  chemical  method  the  oxygen  that  is  loosely  combined  with 
haemoglobin  is  expelled  by  shaking  the  laked  blood  with  potassium 
ferricyanide  (the  oxygen  liberated  during  the  reduction  of  this 
salt  to  ferrocyanide  displaces  the  oxygen  which  is  loosely  com- 
bined with  the  haemoglobin,  and  takes  its  place  to  form  methaemo- 
globin).  The  carbon  dioxide  is  expelled  by  adding  a  non-volatile 
acid  (saturated  solution  of  tartaric  acid).  The  volume  of  the 
expelled  gases  may  be  measured  in  a  suitable  burette,  if  proper 
care  is  exercised  to  avoid  change  in  volume  due  to  variation  in 
temperature.  The  chemical  method  is  the  more  practical  for  most 
work,  but  since  the  gases  become  mixed  with  the  air  originally 
present  in  the  apparatus,  it  is  not  suitable  for  proving  what  these 
gases  may  be.  Logically,  therefore,  in  studying  the  blood  gases 
the  pump  method  should  precede  the  chemical. 

Experiment  52. — The  technique  is  as  follows:  The  water 
jacket  of  the  burette  (Fig.  35)  (G)  and  the  water  bath  of  the  blood 
bottle  (D)  are  filled  with  water  that  has  been  standing  for  some 
time  in  the  same  room,  and  the  temperature  is  noted.  With  the 
stopper  removed  from  the  bottle  the  fluid  (solution  of  calcium 
chloride)  in  the  burette  is  adjusted  to  the  zero  mark  by  raising  or 
lowering  the  levelling  tube  (H).  20  c.c.  of  CCVfree  weak  ammonia 
water*  i§  then  placed  in  the  bottle  (C),  and  2.5  c.c.  (indicated  by  file 
mark)  of  a  freshly  prepared  saturated  solution  of  potassium  ferri- 

*0.5  c.c.  Aq.  Ammonia  per  1000  c.c.  of  distilled  water  to  which  some  barium 
hydroxide  has  been  added  and  then  some  ammonium  sulphate,  the  resulting  pre- 
cipitates of  BaCO3  and  BaSO4  being  allowed  to  settle. 

128 


CHEMICAL  ANALYSIS  OF  BLOOD  GASES. 


129 


FIG.  35.     Haldane's  apparatus  for  analysis  of  blood  by  chemical  method.     (It 
more  satisfactory  to  replace  B  by  a  glass  stopcock). 


130  EXPERIMENTAL  PHYSIOLOGY. 

cyanide  in  the  small  flat-bottomed  tube  (A).  About  15  c.c.  of 
defibrinated  blood  is  exposed  in  a  250  c.c.  flask,  to  alveolar  air 
obtained  by  expiring  deeply  into  the  flask  and  rotating  so  that  the 
blood  forms  a  film  on  the  walls.  The  blood  will  become  saturated 
with  oxygen  and  it  will  take  up  CC>2  until  there  is  equilibrium  be- 
tween the  tensions  of  this  gas  in  the  air  and  blood.  (Is  this  all  the 
CC>2  with  which  the  blood  could  combine?)  The  rotation  should  be 
kept  up  for  about  two  minutes,  the  air  in  the  flask  being  meanwhile 
repeatedly  replaced  by  alveolar  air. 

Immediately  it  has  settled  to  the  bottom  of  the  flask,  10  c.c. 
of  the  blood  is  removed  by  the  pipette  and,  after  wiping  the  tip 
with  a  cloth,  slowly  delivered  under  the  ammonia  solution  in  the 
bottle.  The  bottle  is  then  gently  shaken  until  the  blood  is  com- 
pletely laked  and  a  transparent  red  solution  is  obtained.  (In  cases 
where  the  blood  is  not  saturated  with  oxygen,  as,  for  example,  in 
venous  blood,  it  is  necessary  to  postpone  the  laking  process  until 
after  the  bottle  has  been  closed  and  connected  with  the  burette, 
since  otherwise  C>2  would  be  absorbed  from  the  air) .  Having  placed 
the  flat-bottomed  tube  (A)  upright  in  the  bottle  and  with  the  air 
outlet  of  the  burette  (B)  open,  the  stopper  is  firmly  inserted  into 
the  bottle,  which  is  then  immersed  in  the  water  bath,  and  the  water 
stirred.  Whenever  the  fluid  in  the  burette  ceases  to  move  further — 
indicating  that  the  temperature  of  the  air  in  the  bottle  has  become 
the  same  as  that  of  the  water  bath — the  stopcock  B  is  again  opened 
to  allow  the  meniscus  of  fluid  in  the  burette  to  return  to  the  zero 
mark. 

To  displace  the  oxygen,  the  bottle  is  removed  from  the  water 
bath,  and  while  holding  it  in  a  towel,  to  prevent  its  becoming 
warmed  by  the  hand,  it  is  tilted  so  that  the  ferri cyanide  spills  into 
the  laked  blood.  The  bottle  is  shaken  for  about  one  minute  without 
allowing  the  contents  to  come  in  contact  with  the  stopper  or  tubing. 
The  expelled  oxygen  depresses  the  fluid  in  the  burette,  and  as  it  does 
so,  the  levelling  tube  should  be  lowered  so  that  there  may  not  be 
increased  pressure  in  the  apparatus,  which  would  encourage  leaks. 
The  bottle  is  returned  to  the  water  bath,  and  the  water  stirred 
until  the  level  of  fluid  in  the  burette  remains  constant.  The  reading 
on  the  burette,  taken  when  the  levels  of  fluid  in  it  and  the  levelling 
tube  are  exactly  the  same,  gives  the  c.c.  of  oxygen  expelled  from 


CHEMICAL  ANALYSIS  OF  BLOOD  GASES.  131 

10  c.c.  of  blood.  To  make  certain  that  all  the  oxygen  has  been 
expelled,  the  bottle  is  again  shaken.  The  two  readings  should  agree. 
Great  care  must  be  taken  to  keep  the  apparatus  away  from  drafts 
or  other  influences  that  might  cause  the  temperature  of  the  water 
to  change.  If  this  occurs,  the  temperature  in  the  bath  and  jacket 
must  be  brought  back  to  the  original  temperature  before  the  final 
reading  is  taken.  For  this  purpose  a  small  air  thermometer  T,  in 
the  shape  of  a  U-tube  (containing  coloured  water)  connected 
with  a  test  tube,  (weighted  with  sand)  is  also  placed  in  the  bath. 
If  the  meniscus  of  fluid  in  the  thermometer  changes  during  the 
observation  hot  or  cold  water  must  be  added  to  the  bath  and  this 
stirred  until  the  original  temperature  is  regained. 

The  carbon  dioxide  is  measured  by  a  repetition  of  the  same 
technique,  using  tartaric  acid  in  place  of  ferricyanide  solution. 
The  steps  are  as  follows:  the  stopcock  B  is  opened,  and  the  meniscus 
of  fluid  in  the  burette  brought  back  to  zero  by  raising  the  levelling 
tube,  and  removing  the  stopper  of  the  bottle.  The  reagent  tube  is 
withdrawn  and  washed  into  the  bottle  with  as  small  a  quantity  of 
CCVfree  water  as  possible  (water  that  has  been  boiled  and  cooled). 
2.5  c.c.  of  the  tartaric  acid  solution  is  placed  in  the  tube,  the  stopper 
reinserted  with  stopcock  B  opened,  temperature  adjustment  made, 
and  the  CC>2  displaced  and  measured  by  the  same  manipulations 
as  for  oxygen.  The  bottle  must  be  very  thoroughly  shaken  since 
the  CO2  is  difficult  to  dislodge  from  the  viscid  mixture  of  pre- 
cipitated blood  proteins  now  present  in  the  bottle. 

When  the  estimations  are  completed,  the  flask,  pipette,  bottle, 
reagent  tube,  etc.,  are  washed  thoroughly  clean,  and  any  fluid  that 
may  have  passed  into  the  connecting  tube,  cleaned  out  thoroughly 
with  water  and  a  pipe-cleaner. 


CHAPTER  XVI. 

THE  DISSOCIATION  CURVE  FOR  OXYGEN  AND  THE  CO2- 
COMBINING  POWER  OF  BLOOD. 

For  accurate  determination  of  the  relative  amounts  of  reduced 
and  oxvhemoglobin  in  blood  exposed  to  atmospheres  containing 
varying  partial  pressures  of  oxygen  no  method  surpasses  that  of 
Barcroft  and  his  coworkers.  The  principle  of  this  method  is  to 
expose  a  small  quantity  of  blood  in  a  thin  film  on  the  walls  of  a 
relatively  large  cylindrical  vessel  (tonometer)  containing  a  mixture 
of  nitrogen  and  oxygen  gases  until  equilibrium  has  become  estab- 
lished between  the  partial  pressure  of  the  oxygen  in  the  atmosphere 
and  the  absorption  of  oxygen  by  the  blood.  Some  of  the  blood  is 
transferred  to  a  small  bottle  connected  with  a  differential  mano- 
meter and  shaken  with  dilute  ammonia  water,  whereby  it  becomes 
laked,  and  by  taking  up  oxygen,  causes  shrinkage  in  the  volume  of 
air  in  the  bottle,  the  degree  of  which  is  indicated  by  the  manometer. 
The  oxygen-saturated  blood  is  then  shaken  with  ferricyanide  of 
potassium  which  dislodges  the  oxygen  and  causes  the  pressure  in 
the  bottle  to  rise.  From  the  relative  displacement  of  the  fluid  in 
the  manometer  in  the  two  observations,  the  percentage  saturation 
of  the  blood  with  oxygen  is  readily  calculated. 

For  use  by  a  class  of  students  we  have  found  it  more  expedient 
to  expose  the  blood  to  a  partial  vacuum  instead  of  a  mixture  of 
gases,  the  partial  pressure  of  oxygen  being  readily  calculated 
from  the  degree  to  which  the  tonometer  is  evacuated  as  measured 
by  a  barometer.  This  simplifies  the  technique  by  making  it  un- 
necessary to  analyse  the  gas  in  the  manometer.  For  very  accurate 
work,  however,  mixtures  of  Q%  and  N  are  preferable.  After  exposure 
to  the  partial  vacuum,  the  blood  is  transferred  to  a  differential 
blood  gas  manometer. 
Experiment  53. — The  following  apparatus  is  required: 

THE  TONOMETER  consists  of  a  wide  glass  tube  (the  tonometer  T,  Fig.  36) 
of  fairly  stout  glass,  tapering  down  to  narrow  tubes  at  both  ends.     The  capacity 

132 


DISSOCIATION  CURVE. 


133 


should  be  at  least  200  c.c.*  The  narrow  tubes  are  connected  with  thick-walled 
(pressure)  rubber  tubing  which  should  be  wired  on  to  the  glass  tubes.  The  rubber 
tubes  are  closed  by  screw  clips  (1  and  2).  File  marks  are  made  at  one  of  the 
tapering  ends  of  the  tonometer,  the  distances  between  them  corresponding 
approximately  to  one  cubic  centimeter. 


FIG.  36.  Apparatus  for  the  determination  of  the  Dissocia- 
tion Curve.  (In  place  of  M  the  manometer  shown  in  Fig.  36a 
should  be  used) . 


THE  BAROMETER  consists  of  a  vertical  thick-walled  glass  tube  about  1.25 
metres  long  and  of  about  3  mm.  bore  bent  on  itself  near  one  end,  and  with  the 
other  end  dipping  into  mercury  contained  in  a  wider  flat-bottomed  (specimen) 
tube  (the  mercury  reservoir)  closed  by  a  perforated  cork.  The  barometer  tube 


*It  would  be  preferable  to  use  a  tonometer  twice  as  large  since  this  would 
diminish  errors  due  to  the  addition  of  the  gas  given  off  from  the  blood. 


134 


EXPERIMENTAL  PHYSIOLOGY. 


and  reservoir  are  firmly  mounted  on  a  stand  furnished  with  a  millimeter  scale, 
which  is  attached  to  the  stand  in  such  a  way  that  it  can  be  adjusted  to  bring  its 
zero  to  the  surface  of  mercury  in  the  reservoir,  as  this  varies  at  different  pressures. 
The  free  end  of  the  barometer  tube  is  connected  by  rubber  pressure  tubing  to  a 
glass  T-piece  (A),  one  limb  of  which  is  similarly  connected  to  a  stout-walled 
(filtration)  flask  (F)  joined  to  a  good  water  pump  (P).  A  capillary  tube  closed 
by  a  piece  of  rubber  tubing  and  a  screw  clip  (3)  also  passes  through  the  stopper 
of  the  flask. 

THE  DIFFERENTIAL  MANOMETER. — The  manometer 
shown  in  Fig.  36a  consists  of  a  U-tube  of  capillary 
tubing  furnished  with  3-way  stopcocks  the  side  tubes 
of  which  connect  with  small  bottles.  Suspended  from 
the  stoppers  of  the  bottles  are  small  glass  spoons. 
The  fluid  in  the  manometer  is  clove  oil.  The  mano- 
meter is  mounted  on  a  board  with  a  hook  on  its  back 
by  which  the  board  can  be  hung  on  a  square  glass 
(museum)  jar  containing  water.  The  bottles  should  be 
immersed  in  the  water  up  to  the  necks. 

The  first  step  is  to  rinse  out  the  tono- 
meter with  0.9  per  cent,  saline  and  connect 
it  with  the  side  tube  of  the  barometer  T-piece 
A.  The  pump  P  is  turned  on  with  screw  clips 
1  and  3  closed,  but  screw  clip  2  open  and  the 
pressure  lowered  until  the  mercury  stands  at 
a  constant  level  in  the  barometer.  Screw  clip 
4  is  closed  and  the  mercury  observed,  to  see 
whether  there  is  any  leak.  Provided  there  is 
none,  clip  3  is  cautiously  opened  and  the 
mercury  allowed  to  fall  almost  to  the  level  in  the  reservoir  (R) ; 
clip  2  is  tightened,  the  tonometer,  T,  removed  and  the  pump  turned 
off.  Defibrinated  or  oxalated  blood  (whipped  ox  blood  is  most  suit- 
able for  large  classes,  but  in  any  case  blood  from  an  etherized 
animal  must  not  be  used)  is  now  sucked  into  the  tonometer,  by 
placing  some  of  the  blood  in  a  small  evaporating  dish,  and,  with 
the  rubber  tube  dipping  into  it,  cautiously  loosening  clip  1;  3  to  4 
c.c.  of  blood  should  be  allowed  to  enter  the  tonometer.  This  is 
then  reattached  to  the  T-piece  A  of  the  barometer  and  with  clips 
2  and  4  open  (but  1  and  3  closed)  the  pump  is  turned  on  and  the 
mercury  allowed  to  rise  as  far  as  it  will  go  when  clip  4  is  closed  . 
and  the  pump  turned  off.  Clip  3  is  now  cautiously  opened  until 


FIG.  36A. 


DISSOCIATION  CURVE.  135 

there  is  a  partial  pressure  of  about  20  mm.  Hg.  oxygen  in  the 
tonometer.* 

When  the  mercury  has  reached  this  level,  or  one  near  it,  clip  3 
is  closed  and  the  height  at  which  the  mercury  stands  very  accurately 
noted.  Clip  2  is  closed,  after  which  the  mercury  is  allowed  to  fall 
to  zero  by  opening  3.  The  tonometer  is  removed  and  rotated  so 
that  the  blood  becomes  spread  out  as  a  thin  film  on  the  walls, 
after  which  it  is  placed  in  a  water-bath  kept  about  40°  C.  in  which 
it  is  constantly  rotated  for  about  15  minutes. 

On  removal  from  the  bath  the  pressure  in  the  tonometer  must 
again  be  measured.  For  this  purpose  the  tonometer  is  reattached 
to  A  and  the  pump  is  turned  on  (with  3  closed)  until  the  mercury 
has  risen  to  the  level  at  which  it  previously  stood.  Clip  4  is  closed 
and  2  opened.  If  there  has  been  no  leak,  and  time  has  been  allowed 
for  the  tonometer  to  cool  down,  there  will  be  practically  no  differ- 
ence between  the  two  readings.  If  a  difference  of  more  than  5  mm. 
is  observed  it  must  be  noted  and  the  pressure  prevailing  in  the 
tonometer  taken  as  the  average  between  the  two  readings. 

Meanwhile  3  c.c.  of  freshly  prepared  weak  ammonia  water  con- 
taining a  trace  of  saponin  (0.5  c.c.  aq.  ammonia  in  500  c.c.  water) 
has  been  placed  in  the  blood  gas  bottle.  A  pointed  glass  tube 
about  30  mm.  long  is  now  attached  to  the  rubber  tubing  of  the  tono- 
meter and  this  is  removed  from  the  barometer  and  held  in  a  vertical 


*This  is  computed  as  follows:  After  suitable  adjustment  the  standard  baro- 
meter in  the  room  is  read  and  from  the  reading  is  deducted  the  tension  of  aqueous 
vapour  at  the  temperature  of  the  room  (for  Table,  see  page  277  of  Appendix). 
The  difference  gives  the  pressure  in  mm.  Hg.  of  an  atmosphere  of  dry  air.  Since 
air  contains  20.96  oxygen,  the  partial  pressure  of  this  gas  in  the  tonometer  must  be 

20  96 
equal  to  — : —  ths.  of  the  difference  between  the  height  to  which  the  mercury  is 

-LUU 

raised  in  B  and  the  corrected  barometer  reading.  Thus,  suppose  the  room 
barometer  to  be  753.4  mm.  and  the  temp.  20°  C.,  the  corrected  barometer  reading 
is  753.4-17.4  =  736  mm. 

Then--?6  X736  =  154.2  mm.  02 

-LUU  \ 

20  X  736 

Suppose  a  tension  of  20  mm.  02  is  desired,  then  =  =95.45  mm. 

154 .2 

That  is  the  mercury  in  the  barometer  must  be  raised  to  736  —  95.45  or  640.55  mm. 
above  the  level  in  the  reservoir  (R). 


136  EXPERIMENTAL  PHYSIOLOGY. 

position  above  the  bottle.  The  screw  clip  2  is  opened  so  that  the 
air  enters  the  tonometer,  the  clip  1  is  then  cautionsly  loosened  to 
let  a  drop  or  two  of  blood  flow  out  from  the  tip  of  the  glass  tube,* 
and  after  closing  it  again  the  end  of  the  tube  is  wiped  free  of  blood 
and  placed  in  the  bottle  so  that  it  dips  under  the  ammonia  solution. 
Clip  1  is  now  cautiously  opened  and  about  1  c.c.  of  blood  allowed  to 
flow  under  the  ammonia  water.  If  this  is  done  carefully  the  blood 
does  not  mix  with  the  ammonia  water  but  this  floats  on  the  top  as  a 
layer  and  so  prevents  any  diffusion  of  oxygen  between  the  blood 
and  the  air.  The  bottle  is  firmly  closed  by  its  stopper,  the  stopcock 
being  meanwhile  open  to  the  outside  so  that  the  level  of  the  clove  oil 
in  the  manometer  is  not  disturbed.  The  bottle  must  then  be  sub- 
merged in  a  water-bath  containing  water  at  about  room  tempera- 
ture, in  which  it  is  left  until,  with  the  stopcock  closed,  no  further 
contraction  of  volume,  due  to  cooling,  is  observed  to  occur. 

The  manometer  is  now  removed  from  the  bath  and  vigorously 
shaken  so  that  the  blood  becomes  laked  and  absorbs  C>2  from  the 
atmosphere  of  the  bottle.  On  replacing  the  bottle  in  the  bath  and 
allowing  time  for  cooling  the  difference  between  the  levels  of  clove 
oil  in  the  two  limbs  of  the  manometer  is  noted.  With  the  stopcock 
open  to  the  outside,  the  stopper  is  removed  from  the  bottle  and 
about  0.25  c.c.  of  a  freshly  prepared  saturated  solution  of  potassium 
ferricyanide  is  placed  in  the  glass  spoon  suspended  from  the  stopper 
without  allowing  any  of  the  ferricyanide  to  mix  with  the  laked 
blood.  After  reinserting  the  stopper  and  cooling,  the  bottle  is 
again  removed  from  the  bath  and  shaken  so  that  the  ferricyanide, 
by  mixing  with  the  laked  blood,  drives  off  the  loosely  combined 
oxygen  and  raises  the  pressure,  which  is  measured  by  the  mano- 
meter. 

The  relative  amounts  of  reduced  haemoglobin  and  oxyhaemo- 
globin  present  in  the  blood  are  proportional  to  the  first  and  second 
readings  of  the  manometer;  when  all  is  reduced  haemoglobin  the 
diminished  pressure  (shrinkage)  recorded  in  the  first  shaking  of  the 
bottle  is  the  same  as  the  increased  pressure  recorded  in  the  second. 


*Enough  blood  should  be  run  out  to  bring  the  meniscus  of  blood  in  the  tono- 
meter to  the  upper  file  mark. 


DISSOCIATION  CURVE.  137 

The  calculation  of  the  percentage  saturation  of  haemoglobin 
with  oxygen  is  made  by  subtracting  the  first  reading  from  the 
second,  dividing  by  the  second  reading  and  multiplying  by  100. 
Suppose  in  the  observation  made  at  20  mm.  partial  pressure  of  O2 
the  first  reading  is  24  mm.  and  the  second,  108,  then 
108-24 

77-°%  Hb°  and  22-3%  Hb 


The  result  must  now  be  plotted  on  coordinate  paper  with  the 
percentages  of  HbO  along  the  ordinates  and  the  partial  pressure  of 
Oxygen  on  the  abscissae.  The  experiment  should  be  repeated, 
using  10  mm.  and  40  mm.  pressures  of  oxygen,  and  the  results 
similarly  plotted.  By  joining  the  points,  the  dissociation  curve  for 
blood  is  obtained.  Care  must  be  taken  to  see  that  the  bottle  is 
sufficiently  shaken  so  that  the  partly  reduced  blood  absorbs  all  the 
oxygen  and  gives  it  up  again  with  ferricyanide.  It  is  particularly 
in  the  latter  operation  that  care  must  be  taken. 

The  Influence  of  Carbon  Dioxide  in  Lowering  the  Dissocia- 
tion Curve  can  be  readily  shown  by  the  method.  The  procedure 
is  as  follows:  After  the  pressure  has  been  reduced  to  the  desired 
degree  in  the  tonometer,  the  latter  is  placed  in  a  horizontal  position 
so  that  the  blood  lies  along  the  walls,  free  of  the  ends.  A  CC>2 
generating  apparatus  (Kipp's)  or  a  bottle  containing  this  gas  is 
then  connected  by  suitable  tubing  with  the  free  end  of  the  tono- 
meter, care  being  taken  before  making  the  connection,  to  fill  the 
tubing  with  CCV  To  accomplish  this  a  slow  stream  of  the  gas  is 
maintained  and  the  air  in  the  tubing  beyond  the  screw  clip  (1)  is 
squeezed  out  before  connecting  with  the  CC>2  generator.  The  most 
suitable  partial  pressure  of  CC>2  to  work  with  is  40  mm.  and  to 
attain  it  the  C(>2  apparatus  is  first  of  all  opened  and  the  screw  clip  1 
very  cautiously  loosened  until,  with  clip  2  open  but  3  and  4  closed, 
the  mercury  descends  about  40  mm.  in  the  barometer.  Clips  1  and 
2  are  then  tightly  screwed  down,  and  the  tonometer  removed,  the 
further  procedure  being  exactly  as  described  above. 

The  effect  of  the  40  mm.  of  CO2  will  be  found  in  the  above 
example,  where  a  partial  pressure  of  20  mm.  C>2  was  used,  to  reduce 
the  percentage  of  HbO  from  77  to  about  35. 


138  EXPERIMENTAL  PHYSIOLOGY. 

THE   C02-COMBINING  POWER  OF  THE  ALKALINE 
RESERVE  OF  THE  BLOOD. 

After  completing  the  estimations  necessary  for  finding  the  per- 
centage of  oxy haemoglobin,  in  the  experiments  in  which  CC>2  is 
present  in  the  tonometer,  it  is  of  interest  to  determine  the  amount 
of  this  gas  with  which  the  blood  has  combined.  This  will  repre- 
sent its  ability  to  act  as  a  buffer  towards  foreign  acids.  To  perform 
the  estimation  it  is  necessary,  however,  to  measure  accurately  the 
amount  of  blood  which  is  removed  from  the  tonometer  to  the  blood 
gas  bottle.  This  can  readily  be  done  by  attaching  a  1  c.c.  pipette 
to  the  tubing  of  the  tonometer  (beyond  clip  1),  a  few  drops  of  blood 
being  allowed  to  escape  from  the  pipette  before  delivering  under 
the  ammonia  solution  in  the  bottle,  and  precautions  being  taken 
not  to  remove  any  of  the  upper  layers  of  blood  that  had  been  exposed 
to  full  atmospheric  pressure  when  the  tonometer  was  opened. 
This  is  ensured  by  removing  the  pipette  from  the  tonometer  before 
all  the  blood  has  run  out. 

To  dislodge  the  CO2  from  the  blood,  the  stopper  is  removed 
with  the  usual  precautions  and  about  0.25  c.c.  of  a  saturated  solution 
of  tartaric  acid  placed  in  the  small  test  tube.  After  closing  and 
allowing  for  temperature  changes,  the  acid  is  shaken  with  the 
mixture  of  blood  and  ferricyanide,  and  the  CO2  thereby  evolved, 
measured  by  multiplying  the  displacement  of  the  fluid  in  the 
manometer  by  a  figure  (the  constant  of  the  apparatus)  obtained  by 
a  preliminary  experiment  in  which  a  known  amount  of  a  standard 
carbonate  solution  is  similarlv  treated. 


SECTION  V 
SPECIAL   SENSES. 
CHAPTER   XVII. 

VISION. 

In  order  to  gain  accurate  information  through  the  sense  of  sight 
about  objects  in  the  external  world,  their  size  and  shape,  and 
their  positions  relative  to  one  another,  two  things  are  necessary. 
There  must  in  the  first  place  be  a  group  of  cells  sensitive  to  light 
waves  and  so  connected  to  the  central  nervous  system  that  stimu- 
lation of  any  part  of  the  sensitive  surface  gives  rise  to  a  sensation 
different  from  that  caused  by  stimulation  of  any  other  part. 
Secondly  some  system  of  lenses  is  needed  so  that  each  point  in 
the  sensitive  layer  does  not  receive  rays  from  all  directions  in  the 
external  field,  but  has  focussed  on  it  only  those  which  arise  from  a 
single  part  of  the  field.  In  the  eye  the  sensitive  elements  are  con- 
tained in  the  retina,  and  the  cornea  and  lens  together  make  up  the 
focussing  apparatus.  In  the  discussion  and  experiments  which 
follow  we  shall  first  consider  the  way  in  which  light  waves  are 
brought  to  a  focus  in  the  eye  and  later  the  response  of  the  retina 
to  them.  Before  taking  up  the  complex  arrangement  of  refracting 
surfaces  which  exist  in  the  eye  it  is  well  to  review  some  of  the  simple 
cases  of  the  formation  of  images  both  by  lenses  and  by  mirrors. 
Although  the  focussing  in  the  eye  is  entirely  done  by  refracting 
surfaces  and  reflection  plays  no  part  in  it,  it  is  by  reflected  rays 
that  one  examines  the  condition  of  the  eye  and  on  this  account 
it  is  necessary  to  have  clearly  in  mind  the  laws  which  underlie  the 
reflection,  as  well  as  those  of  refraction. 

Physiological  Optics. 
Reflection. 

When  rays  of  light  diverging  from  a  point  are  reflected  by 
a  mirror  their  course  is  so  changed  that  they  appear  to  an  observer 

139 


140 


EXPERIMENTAL  PHYSIOLOGY. 


to  come,  not  from  the  actual  object  itself,  but  from  some  other  point 
known  as  the  IMAGE  of  that  object.  Each  point  on  a  luminous 
object  has  a  point  image  corresponding  to  it.  The  position  of  the 
image  of  the  whole  object  may  be  found  by  defining  the  position 
of  the  image  of  each  of  its  extreme  or  limiting  points.  To  find  these 
one  applies  the  LAWS  OF  REFLECTION,  which  state  (1)  that  the  inci- 
dent ray  (that  is,  the  ray  before  reflection),  the  reflected  ray,  and 
the  perpendicular  to  the  surface  at  the  point  of  incidence,  are  all 
in  one  plane,  and  (2)  that  the  angle  between  the  incident  ray  and 


FIG.    37.     To  illustrate  the  formation  of  an  image  by  a  plane  mirror. 

the  perpendicular  (or  the  ANGLE  OF  INCIDENCE)  is  equal  to  that 
between  the  perpendicular  and  the  reflected  ray  (the  ANGLE  OF 
REFLECTION).  Fig.  37  shows  the  construction  for  a  plane  mirror. 
PQ  is  the  object,  PA  and  PB,  incident  rays,  and  AE  and  BF,  the 
perpendiculars  to  the  surface  at  the  points  of  incidence.  These, 
together  with  the  reflected  rays,  AC  and  BD,  are  all  in  the  plane 
of  the  paper,  i  and  i'  are  the  angles  of  incidence.  After  reflection 
the  rays  AC  and  BD  pass  in  such  a  direction  as  to  make  each 
angle  of  reflection  equal  to  the  corresponding  angle  of  incidence 
(r  =  i,  r'  =  i'.)  These  rays  both  appear  to  come  from  a  single  point 


PHYSIOLOGICAL  OPTICS. 


141 


behind  the  mirror  P',  the  position  of  which  is  found  by  projecting 
the  lines  of  the  reflected  rays  AC  and  BD  back  until  they  meet. 
Since  ALL  rays  from  the  point  P  on  the  object  appear  after  re- 
flection to  come  from  one  point  on  the  image,  P',  the  place  from 
which  two  of  the  rays  seem  to  come,  must  be  the  apparent  source  of 
all  the  others,  in  other  words,  P'  must  be  the  image  of  the  point  P. 
The  construction  for  Q  is  similar,  Q'  being  its  image.  When  the 


FIG.    38.     To  illustrate  the  formation  of  an  image  by  a  concave  mirror. 


reflected  rays  only  appear  to  come  from  the  image,  as  in  these 
cases,  and  do  not  actually  pass  through  it,  the  image  is  called  a 
VIRTUAL  one.  It  will  be  noted  that  it  is  erect. 

Fig.  38  shows  the  construction  for  reflection  of  a  similar  object  by 
a  concave  mirror.  C  is  the  centre  of  curvature  of  the  mirror;  any 
line  from  C  to  the  surface  is  perpendicular  to  it,  since  it  lies  on  one 
of  the  radii.  One  ray  from  P,  passing  through  C  on  its  way  to  the 


142 


EXPERIMENTAL  PHYSIOLOGY. 


surface,  lies  along  such  a  line.  It  is  reflected  back  along  the  path 
on  which  it  came  (since  i  =  o  in  this  case,  r  must  also  =o).  PA, 
another  incident  ray  from  P,  is  so  reflected  (ray  AB)  that  the  angle 
of  incidence  (i)  equals  the  angle  of  reflection  (r).  The  place  (P') 
where  this  crosses  the  reflected  ray  PC  is  the  image  of  the  point  P, 
from  which  these  and  all  other  reflected  rays  from  P  appear  to 


M 


FIG.  39.    To  show  refraction  of  rays  passing  from  air  into  water. 

come.  The  construction  of  the  image,  Q',  of  the  other  limiting 
point,  Q,  is  similar.  The  rays  in  this  case  actually  pass  through 
the  image  from  which  they  seem  to  come,  and  the  image  is  there- 
fore called  a  REAL  one.  Real  images  are  always  inverted. 

Refraction. 

Refraction  at  a  Plane  Surface. — When  a  ray  of  light  passes 
from  air  into  a  denser  medium  such  as  glass  or  water,  the  direction 


PHYSIOLOGICAL  OPTICS.  143 

in  which  it  travels  is  altered  and  it  is  bent  toward  the  perpendicular 
to  the  surface  between  the  two  media  (Fig.  39).  The  angle  between 
the  incident  ray  and  the  perpendicular  is  the  angle  of  incidence 
(i  and  i'),  that  between  perpendicular  and  refracted  ray,  the  angle 
of  refraction  (r  and  r').  The  extent  to  which  this  bending  or 
REFRACTION  occurs  depends  on  two  things.  One  is  the  angle  of 
incidence.  The  greater  this  angle  is,  the  more  the  ray  is  refracted, 
provided  of  course  that  the  medium  is  the  same.  The  other  factor 
is  the  nature  of  the  medium;  the  denser  the  medium  the  more  it 
refracts.  It  is  found  that  for  a  given  medium  there  is  a  constant 
relationship  between  the  direction  of  the  incident  ray  and  that  of  the 
refracted  one ;  the  sine  of  the  angle  of  incidence  divided  by  the  sine  of 
the  angle  of  refraction  is  always  the  same  for  the  same  medium, 
greater  when  the  medium  is  dense  and  less  when  it  is  rare.  It  is 
usual  to  express  the  refracting  power  of  a  medium  in  this  way  and 
to  call  it  the  REFRACTIVE  INDEX,  designated  by  ju.  The  example  in 
Fig.  39  will  make  this  clear.  AC  and  AI  are  incident  rays, 
CD  and  IJ,  the  rays  after  refraction.  The  angles  of  incidence  are 
i  and  i',  the  angles  of  refraction,  r  and  r'. 

Sine  of  angle  of  incidence 

c^ r i r — r 7- —   =  M  f°r  water  =  1.3; 

Sine  of  angle  of  refraction 

BE 

BC  BE  GH 

that  is  —  or  (since  BC  =  CD)   —  =1.3.     Similarly  —   =1.3. 
L>r  Dr  J  rv. 

CD 

The  ray  ALM,  being  perpendicular  to  the  surface,  is  not  refracted 
but  passes  through  unchanged  in  direction. 

If  the  direction  of  the  light  is  reversed  and  if  it  passes  from  the 
dense  to  the  rare  medium  the  direction  of  refraction  is  also  reversed, 
the  rays  being  bent  away  from  the  perpendicular  instead  of  towards 
it. 

Refraction  at  a  Convex  Surface. — It  is  through  a  convex  re- 
fracting surface  that  the  light  first  passes  on  entering  the  eye,  as  it 
goes  from  the  air  into  the  layer  of  tears  and  the  cornea. 

The  central  point  on  a  curved  refracting  surface  is  called  its 
PRINCIPAL  point  (P.P.  Fig.  40) ;  a  line  joining  this  with  the  centre 
of  curvature  (N.P.)  is  the  principal  axis  of  the  refracting  surface 


(P. A.).  That  ray  from  the 
object  which  is  directed 
straight  towards  the  centre 
of  curvature  or  NODAL  POINT 
(N.P.)  of  the  refracting  sur- 
face lies  of  necessity  on  one  of 
the  radii  to  the  surface;  it  is 
therefore  perpendicular  to  it 
and  is  not  refracted  (ray  2). 
If  a  pencil  of  rays  are  parallel 
to  one  another  and  also 
parallel  to  the  principal  axis 
(see  ray  1),  they  are  all 
brought  to  a  focus  after  re- 
fraction at  some  point  on  the 
axis,  this  point  being  known 
as  the  SECOND  PRINCIPAL 
FOCUS  (P.F2,  Fig.  40).  This 
lies  nearer  the  surface  if  the 
curvature  on  the  surface  is 
sharp  and  the  refractive  index 
high,  farther  back  if  the  sur- 
face is  part  of  a  large  circle, 
or  if  the  refractive  index  of 
the  medium  is  not  very  great. 
Light  to  be  parallel  must  in 
theory  come  from  objects  at 
an  infinite  distance.  In  actual 
fact,  however,  rays  from 
points  more  than  about  ten 
metres  away  diverge  so  little 
that,  for  the  eye  at  least, 
there  is  no  practical  differ- 
ence between  their  focus  and 
that  of  rays  which  arise  from 
further  away.  All  parallel 
rays  which  reach  the  surface 
inclined  at  a  small  angle  to 
the  principal  axis  are  brought 


PHYSIOLOGICAL  OPTICS.  145 

to  a  focus  at  some  point  in  the  plane  of  the  principal  focus  or  the 
PRINCIPAL  FOCAL  PLANE  (P. P.P.).  Rays  which  are  appreciably 
divergent  when  they  reach  the  surface  (that  is  which  arise  from 
objects  less  than  about  ten  metres  away)  have  their  foci  behind 
the  principal  focal  plane.  The  focus  moves  farther  back  the  nearer 
the  object  is  brought  until  finally  a  position  of  the  object  is  reached 
such  that  the  rays  from  it  after  being  refracted  meet  only  at  in- 
finity, that  is,  they  are  parallel  to  one  another.  This  position  is 
known  as  the  first  principal  focus  (P.P.  Fig.  40).  If  the  object  is 
brought  nearer,  the  rays  are  merely  rendered  less  divergent  after 
refraction  and  are  not  brought  to  a  focus  at  all. 

Fig.  40  shows  the  way  in  which  the  position  may  be  found  of  an 
image  formed  by  refraction  at  such  a  surface.  From  each  limiting 
point  on  the  object,  any  two  rays,  the  paths  of  which  are  known,  are 
followed  until  they  meet.  The  place  where  they  cross  is  the  image 
of  the  point  from  which  they  arise. 

Refraction  by  a  Convex  Lens. — Rays,  after  they  have  entered 

the  eye,  have  to  pass  through  a  convex  lens,  the  crystalline  lens, 

before  they  reach  the  light-sensitive  cells.    The  refraction  in  this 

case  is  similar  to  that  which  we  have  just  considered;  like  a  simple 

convex  surface,  a  convex  lens  converges  rays  which  pass  through  it. 

The  extent  of  the  refraction  depends  on  how  sharply  the  surfaces  of 

the  lens  are  curved  and  on  how  much  denser  its  substance  is  than 

the  surrounding  medium.     The  lens  has  a  principal  axis,  which 

joins  the  centres  of  curvature  of  the  two  surfaces,  a  first  and  second 

principal  focus,  and  a  principal  focal  plane.     The  point  where  the 

principal  axis  cuts  the  surfaces  is  the  principal  point;  rays  which 

pass  through  here  are  not  appreciably  bent  if  the  lens  is  a  thin  one. 

Experiment  54.— Set  in  front  of  the  opening  of  the  lantern  the 

ground  glass  screen,  and  the  diaphragm  with  a  vertical  slit. 

Through  a  convex  lens  throw  an  image  of  the  slit  on  the  black 

wooden  block.    The  slit  is  to  serve  as  the  "object".    Now  place 

against  the  lens  a  sheet  of  paper  perforated  with  two  holes, 

about  3  mm.  in  diameter,  horizontally  placed  and  less  than  the 

diameter  of  the  lens  apart.     This  stops  all  but  two  pencils  of 

rays  from  the  object.    Note  that  the  image  does  not  disappear, 

but  becomes  less  bright.     Cover  one  hole  and  see  the  further 

dimming  of  the  image. 


146  EXPERIMENTAL  PHYSIOLOGY. 

Move  the  object  further  from  the  lens.  There  are  now  two 
blurred  images  of  the  object.  Cover  the  left  hole  and  note 
that  one  image  disappears. 

Place  the  object  at  a  distance  from  the  lens  less  than  the 
first.  Note  that  in  this  case  also  a  double  image  is  formed. 
Again  cover  the  left  hole  and  see  whether  the  image  which  dis- 
appears is  the  same  one  as  before. 

Draw  diagrams  of  the  formation  of  images  by  the  lens  when 

the  object  is  (a)  at  a  distance  from  which  the  rays  are  focussed 

on  the  screen,  (b)  at  a  greater  distance,  (c)  at  a  less  distance. 

Show  whether  the  image  in  each  case  is  real  or  virtual. 

Since  the  focal  length  of  a  lens  varies  inversely  as  its  strength, 

being  shorter  the  stronger  the  lens,  it  is  usual  to  express  the  strength 

of  a  lens  in  terms  of  the  reciprocal  of  its  focal  length.    The  standard 

is  a  lens  which  has  a  focal  length  of  one  metre  and  this  is  said  to 

have  a  strength  of  one  dioptre  (D  =  ^r,  where  F  =  focal  length, 

r 

D  =  strength  in  dioptres). 

Refraction  in  the  Eye. 

If  the  rays  from  an  object  pass  in  their  course  through  a  succession  of  focussing 
surfaces,  a  calculation  of  the  position,  size,  etc.,  of  the  image  which  they  finally 
form  can  be  made  along  the  lines  which  we  have  indicated  as  long  as  the  surfaces 
are  only  two,  or  at  most  three,  in  number.  When  they  are  more  than  that  the 
problem  becomes  unwieldly.  In  such  a  case,  however,  it  is  often  possible  by 
mathematical  calculation  to  arrive  at  an  ideal,  or  imaginary,  single  convex  refract- 
ing surface  which  will  have  approximately  the  same  power  as  that  of  all  the 
surfaces  together.  For  this  the  radii  of  curvature  and  the  refractive  indices  of  all 
must  be  known  and  the  surfaces  must  be  "centred".  Surfaces  are  said  to  be 
centred  when  they  all  lie  along  the  same  principal  axis.  Light  entering 
the  eye  has  to  pass  through  a  large  number  of  refracting  surfaces, 
through  cornea,  aqueous  humour,  lens,  and  vitreous  humour.  Of  these, 
the  cornea,  the  aqueous  humour  and  the  vitreous  humour  have  refractive  indices 
which  are  much  alike,  all  about  equal  to  that  of  water  (ju  =  1.3).  The  lens  is 
denser  and  all  parts  of  it  have  not  the  same  composition.  It  is  made  up  of  more 
or  less  concentric  layers  about  a  central  core  and  the  density  increases  from  the 
outer  layers  (ju  =  1.40)  to  the  core  (//  =  !. 44).  When  they  enter  the  cornea  from 
the  air,  light  rays  undergo  the  main  part  of  the  refraction  which  occurs  in  the  eye, 
because  the  densities  of  the  two  media  are  so  different.  The  other  con- 
siderable refraction  occurs  on  the  passage  of  the  rays  through  the  denser  substance 
of  the  crystalline  lens.  In  the  complex  system  of  the  eye  the  refractive  index 


PHYSIOLOGICAL  OPTICS.  147 

and  the  radius  of  curvature  of  each  part  is  known  and  the  surfaces,  although 
not  accurately  centred,  are  sufficiently  nearly  so  to  make  it  possible  to  find 
mathematically  a  single  surface  which  represents  the  whole.  This  is  used  in  the 
construction  of  the  SCHEMATIC  EYE  (Fig.  41).  The  single  refracting  surface  is  made 
to  lie  a  few  millimetres  behind  the  real  cornea.  In  the  unaccommodated  eye 
distant  objects  are  clearly  seen,  which  must  mean  that  the  rays  from  them,  which 
are  parallel  or  nearly  so,  form  sharp  images  on  the  light-sensitive  surface.  The 
refracting  surface  of  the  schematic  eye,  to  represent  this,  has  its  principal  focal 
plane  on  the  retina.  From  a  distant  point  object  situated  in  any  part  of  the 
visual  field,  we  know  the  course  of  one  ray,  that  which  is  directed  straight  for  the 
nodal  point  of  the  simplified  eye  and  which  is  not  changed  in  its  direction  before 
reaching  the  retina.  By  the  previous  argument  we  have  shown  that  all  rays  from 
such  a  point  meet  at  the  retina.  Therefore  to  find  the  image  on  the  retina  of  any 
object,  all  we  need  to  do  is  to  draw  straight  lines  from  its  limiting  points  through 
the  nodal  point  of  the  schematic  eye. 


FIG.  41.     The  formation  of  an  image  by  the  eye  as  represented  by  the  schematic  eye. 

It  will  be  seen  that  according  to  the  foregoing  construction  the 
retinal  image  is  an  inverted  one.  That  we  interpret  this  to  our- 
selves as  an  erect  picture  of  the  object  may  at  first  sight  appear  con- 
fusing. It  should  be  remembered,  however,  that  we  are  not  born 
with  the  faculty  of  associating  stimulation  of  any  particular  part 
of  the  retina  with  the  presence  of  some  object  in  a  particular  part 
of  the  external  world.  We  learn  this  in  infancy  through  our  other 
senses,  mainly  the  sense  of  touch.  Because  a  point  on  one  side  of 
the  retina  is  as  a  matter  of  fact  always  affected  by  light  from  some 
object  which  we  know  by  our  other  senses  to  be  on  the  opposite 
side  of  the  field,  we  form  the  habit  of  interpreting  the  stimulation 
in  this  way.  We  associate  stimulation  of  the  right  side  of  the  retina 
with  the  presence  of  something  in  the  left  side  of  the  visual  field 
and  so  on.  To  put  the  matter  more  generally,  we  refer  stimulation 
of  any  part  of  the  retina  to  the  presence  of  some  object  in  the  out- 


148  EXPERIMENTAL  PHYSIOLOGY. 

side  world  situated  along  the  line  which  joins  that  part  with  the 

nodal  point  of  the  eye.     That  this  is  actually  the  case  may  be  seen 

from  the  following  experiment. 

Experiment  55. — Close  the  right  eye  and  direct  the  eyes  as  far  as 
possible  to  the  left.  With  the  tip  of  the  finger  press  lightly  on 
the  right  eye  at  different  points  near  the  margin  of  the  orbit 
and  note  the  positions  in  the  visual  field  of  the  resulting  "phos- 
phenes". 
In  this  experiment  although  we  press  the  right  side  of  the  retina 

all  the  light  spots  which  we  see  appear  to  be  on  our  left,  in  the  upper 

field  if  we  press  below  and  in  the  lower  if  we  press  on  the  upper  part 

of  the  eyeball. 


CHAPTER    XVIII. 
ERRORS  IN  REFRACTION. 

PHYSIOLOGICAL  ERRORS.     ACCOMMODATION. 
SPHERICAL  ABERRATION. 

In  the  description  of  refraction  by  lenses  it  has  been  stated  that 
a  spherical  lens  brings  all  the  rays  from  one  point  on  the  object  to 
a  focus  at  the  same  point.  As  a  matter  of  fact  this  is  not  strictly 
speaking  the  case.  The  rays  which  pass  through  the  outer  parts 
of  the  lenses  are  more  refracted  than  those  nearer  the  centre;  they 
are  therefore  brought  to  a  focus  a  little  in  front  of  the  central  ones, 
and,  passing  on,  blur  the  image  which  the  latter  form.  The  differ- 
ence between  the  foci  becomes  greater  the  nearer  the  object  and  the 
more  divergent  the  rays  from  it. 

>j  Experiment  56. — Fill  the  bottle  with  water  and  use  it  as  a  lens.* 
Cover  the  opening  in  the  lantern  by  the  diaphragm  with  a 
2  mm.  opening,  and  set  it  about  a  meter  away  from  the  bottle. 
Move  the  black  screen  in  the  pencil  of  light  coming  through  the 
lens  until  you  have  the  light  as  sharply  focussed  on  it  as  possible. 
Note  that  the  region  on  either  side  of  the  focus  is  dimly  lighted. 
Interrupt  the  light  coming  through  the  outer  parts  of  the  lens 
and  note  that  the  focus  becomes  sharper.  Bring  the  lantern 
nearer  the  lens,  set  the  screen  at  the  new  focus  and  interrupt 
the  outer  refracted  rays  as  before.  The  improvement  in  the 
sharpness  of  focus  is  more  marked. 

Cover  the  round  opening  of  the  optical  box  with  the  clear 
glass  slide.  Set  the  bottle  immediately  inside  the  opening,  light 
the  incense  in  the  cork  and  cover  the  box.  When  it  has  filled 
with  smoke  place  the  lantern  about  a  meter  away,  so  that  the 


*The  lens  in  this  case  is  of  course  a  cylindrical  one.  Since,  however,  we  have 
to  do  only  with  those  rays  which  diverge  horizontally,  we  may  use  the  refraction 
which  the  curved  surface  effects  in  these  to  represent  refraction  by  any  one  plane 
of  a  spherical  lens. 

149 


150  EXPERIMENTAL  PHYSIOLOGY. 

rays  pass  through  the  bottle,  and  look  directly  down  on  the 
refracted  rays.    The  boundaries  of  the  light  pencil  are  curved, 
and  not  plane,   surfaces  because  the  outer  rays,  being  more 
refracted  than  the  inner,  intersect  the  latter.    Move  the  lantern 
nearer  and  note  that  the  curvature  of  the  surfaces  increases. 
The  refraction  in  the  eye  is  corrected  for  spherical  aberration  to 
some  extent  by  the  difference  in  the  refractive  indices  of  the  differ- 
ent parts  of  the  lens.     The  central  rays  pass  through  the  part  of 
the  lens  which  is  the  most  dense  and  so  they  are  refracted  more,  in 
comparison  with  the  rays  through  the  periphery,  than  they  would 
be  if  all  the  layers  were  of  the  same  composition. 

Chromatic  Aberration. — Light  which  arises  from  objects  seen 
under  ordinary  circumstances  is  made  up  of  waves  of  different 
lengths.    In  passing  through  the  refracting  media  each  wave  length 
is  bent  to  a  slightly  different  extent  and  this  causes  another  error  in 
the  refraction  of  the  eye.    The  shorter  waves  of  the  violet  end  of 
the  spectrum  are  brought  to  a  focus  nearest  the  lens,  the  long  ones 
of  the  red  end  are  least  refracted,  while  the  foci  of  those  of  inter- 
mediate length  lie  between  these  two  extremes.* 
Experiment  57. — Chromatic  Aberration  in  Refraction  by  a 
Convex  Lens. — Set  in  front  of  the  opening  of  the  lantern  the 
ground  glass  screen  and  the  diaphragm  with  a  2  mm.  opening. 
Place  the  block  holding  the  convex  lens  about  15  cm.  from  the 
opening.     Using  a  sheet  of  paper  as  a  screen  move  it  back  and 
forth  in  the  path  of  the  refracting  light  until  you  find  the  focus. 
Note  that  it  is  not  pure  white,  but  made  up  of  coloured  bands. 
Cover  the  right  half  of  the  lens  with  a  card.     The  light  has 
violet  fringe.     Uncover  the  lens  and  move  the  screen  a  little 
nearer  to  it.     The  disc  has  a  violent  centre  and  red  border. 
Move  the  screen  beyond  the  focus.    The  colours  of  the  disc  are 
reversed. 

Experiment  58. — Chromatic  Aberration  in  the  Eye. — Cover 
with  a  card  the  outer  half  of  the  right  pupil  and,  closing  the 
left  eye,  look  at  an  electric  light  filament.  It  appears  to  have 
a  red  border  at  the  right  and  a  violet  one  at  the  left.  Draw  a 

*For  the  way  in  which  chromatic  aberration  is  done  away  with  in  lenses  of  fine 
optical  instruments  by  using  layers  of  different  dispersive  power,  the  student 
is  referred  to  his  text-books  on  Light.  There  is  no  such  adjustment  in  the  eyr« 


ERRORS  OF  REFRACTION  AND  ACCOMMODATION.  151 

diagram  of  the  course  of  the  red  rays  and  of  the  violet  ones, 

using  the  schematic  eye,  and  explain  the  apparent  contradiction 

between  the  results  of  this  and  of  the  preceding  experiment. 

When  we  turn  our  eyes  to  look  at  a  certain  object  we  habitually 
place  them  so  that  the  image  falls  on  the  fovea  centralis.  This  is  the 
part  of  the  retina  which  is  capable  of  seeing  most  acutely,  of  making 
out  differences  smaller  than  can  be  perceived  by  any  other  part,  and 
the  line  which  connects  it  with  the  nodal  point  is  called  the  VISUAL 
AXIS.  If  this  corresponded  with  the  optical  axis  the  refraction 
would  be  the  best  that  the  refracting  media  of  the  eye  are  capable 
of.  In  point  of  fact,  however,  there  is  an  angle  of  about  5°  between 
the  two  and  this  is  a  slight  additional  source  of  error  in  refraction 
in  the  eye. 

ERRORS  TENDING  TO  BE  PATHOLOGICAL. — The  defects  in  refraction  which  have 
been  described  so  far  are  found  in  every  eye.  As  well  as  these  there  are  several 
types  of  faulty  formation  of  images  which  are  often  found,  any  one  of  which  if 
it  is  at  all  pronounced  makes  the  vision  of  the  eye  abnormal. 

NEAR-SIGHTEDNESS  OR  MYOPIA. — In  near-sighted  eyes  light  from  distant 
objects,  that  is  for  practical  purposes  parallel  light,  is  brought  to  a  focus  in  front 
of  the  retina  instead  of  exactly  on  it.  The  rays  therefore  when  they  reach  the 
retina  are  already  diverging  from  their  focus  and  they  form  a  blur  on  the  light- 
sensitive  layer  instead  of  a  sharp  point  of  light  (Fig.  42  B.).  This  may  be 
because  the  curvature  of  one  or  all  of  the  refracting  surfaces  is  unusually  sharp,  the 
length  of  the  eyeball  being  normal,  or  it  may,  as  is  more  frequently  the  case,  be 
due  to  an  unusual  length  of  the  eyeball.  There  is  no  physiological  correction  for 
this  condition.  In  practice  it  is  rectified  by  placing  in  front  of  the  eye  a  ccncave 
lens.  Light  from  distant  objects  is  thus  made  divergent  before  it  reaches  the  eye 
and  its  focus  therefore  lies  on  the  retina,  further  back  than  the  principal  plane  of 
the  shortsighted  eye. 

In  LONG-SIGHTEDNESS  OR  HYPERMETROPIA  the  condition  is  reversed.  The 
principal  focus  of  the  refracting  media  lies  behind  the  retina  and  the  parallel  rays 
from  distant  objects  have  not  yet  arrived  at  their  focus  when  they  are  interrupted 
by  it  (Fig.  42,  C.).  An  increase  in  the  refractive  power  of  the  eye 
is  needed  to  bring  the  focus  forward  and  give  a  clear  image.  An  effort  of  contin- 
ued accommodation  (see  below)  will  accomplish  this,  but  such  an  effort  gives  rise 
to  various  nervous  symptoms,  headache,  irritability  and  the  like.  If  convergent 
glasses  of  suitable  strength  are  used,  the  focus  may  be  advanced  the  necessary 
amount  without  any  effort  on  the  part  of  the  patient. 

ASTIGMATISM.  So  far  as  we  have  considered  the  eye  as  refracting  all  rays  to 
the  same  extent  no  matter  in  what  plane  they  diverge  from  their  object  nor 
whether  they  pass  through  the  upper  and  lower  parts,  or  through  the  right  and 
left  sides,  of  the  refracting  surfaces.  Cases  are  fairly  common,  however,  in  which 
this  does  not  hold  good.  In  these  eyes,  known  as  astigmatic,  all  the  meridians 


152 


EXPERIMENTAL  PHYSIOLOGY. 


are  not  curved  alike.  In  the  most  common  form  the  vertical  meridian  is  an  arc  of  a 
smaller  circle  than  is  the  horizontal  and,  being  more  sharply  curved,  it  refracts 
more  than  does  the  latter.  Rays  which  diverge  in  a  vertical  plane  from  a  point 


T.T. 


FIG.  42.  The  focussing  of  parallel  rays  from  a  distant  object  by  (A)  a 
normal,  (-B)e.  short-sighted  and  (C)  a 'long-sighted  eye.  PF  in  each  case  shows  the 
position  of  the  principal  focus  of  the  combined  refracting  surfaces  of  the  eye, 
represented  by  the  single  surface  of  the  schematic  eye. 


object  are  brought  to  a  focus  by  such  eyes  in  front  of  the  focus  for  the  horizontal 
rays.  The  result  is  that  the  eye  can  never  see  a  point  image  of  a  point  object. 
If  the  rays  through  one  meridian  are  focussed  on  the  retina  then  those  which  pass 
through  the  meridian  at  right  angles  to  the  first  must  reach  the  retina  as  a  pencil 


ERRORS  OF  REFRACTION  AND  ACCOMMODATION.  153 

of  rays,  either  because  they  have  already  passed,  or  because  they  have  not  yet 
reached  their  focus.  The  unlike  meridians  are  not  necessarily  arranged  in  this 
way,  the  vertical  is  not  always  that  of  greatest  curvature,  although  this  is  the  most 
common  form,  nor  are  the  meridians  which  differ  most  always  at  right  angles  to 
one  another.  When  they  are  the  astigmatism  is  a  REGULAR  one;  when  the  angle 
between  is  not  a  right  angle  it  is  an  IRREGULAR  astigmatism.  Regular  astig- 
matism is  easy  to  correct  by  glasses  ground  so  as  either  to  converge  the  rays  which 
are  to  pass  through  the  meridian  of  least  refractive  power  or  to  render  more 
divergent  those  directed  towards  the  meridian  of  greater  refractive  power. 
Irregular  astigmatism  is  more  difficult  to  correct.  In  some  eyes  the  astigmatism 
is  of  neither  of  these  types  but  consists  in  irregularities  in  the  curvature  of  the 
same  meridian,  a  condition  which  cannot  be  made  right  with  glasses.  Even  in  a 
normal  eye  there  is  something  of  this  irregularity.  The  image  of  a  star  is  not  a 
single  point,  as  it  would  be  if  the  refracting  surfaces  were  of  even  curvature 
throughout,  but  it  has  an  irregular  shape  which  is  different  for  each  individual, 
because  of  the  slight  defects  in  the  curves  of  the  various  surfaces. 

Accommodation. — AVe  have  seen  how  parallel  rays  from  a  dis- 
tant object  are  brought  to  a  focus  on  the  retina  of  a  normal  eye. 
When  however  the  gaze  is  directed  to  an  object  close  at  hand  the 
eye  receives  rays  which  diverge  from  one  another  by  a  considerable 
angle.  If  no  change  takes  place  in  the  refractive  power  of  either 
cornea  or  lens  these  rays  tend  after  refraction  towards  a  focus 
lying  behind  the  retina.  In  consequence  when  they  are  intercepted 
by  the  retina  they  form  a  blur  and  not  a  sharp  point.  To  make  the 
image  of  the  near  object  a  clear  one  either  the  distance  between 
retina  and  lens  must  be  made  greater  than  it  is  for  distant  vision, 
just  as  one  increases  the  distance  between  lens  and  plate  in  a 
camera  when  focussing  for  objects  close  at  hand,  or  else  the  refrac- 
tion by  the  eye  media  must  be  increased.  The  latter  is  the  change 
which  is  brought  about  in  the  mammalian  eye  by  the  act  of  accom- 
modation. The  curvature  of  the  anterior  surface  of  the  lens  is 
made  sharper  and  its  refraction  therefore  greater. 

To  understand  the  most  generally  accepted  explanation  of  the  way  in  which 
this  is  done,  one  must  have  clearly  in  mind  the  anatomical  relationship  which  the 
lens  bears  to  neighbouring  structures  in  the  eye  (Fig.  43).  It  is  held  in  its  place 
by  the  numerous  fibres  which  together  make  up  the  suspensory  ligament  of  the 
lens.  These  are  more  or  less  radially  arranged  about  the  lens,  being  continuous 
at  their  inner  ends  with  the  capsule  near  the  margin,  while  the  outer  ends  of  the 
threads  are  connected  to  the  surface  of  the  ciliary  body  near  its  free  inner  edge 
throughout  its  entire  circle.  The  arrangement  is  such  that  those  fibres  which 
come  from  the  posterior  surface  of  the  lens  capsule  go  to  the  anterior  surface  of  the 
ciliary  body  and  those  which  arise  from  the  anterior  surface  of  the  lens  are  at- 


154 


EXPERIMENTAL  PHYSIOLOGY. 


tached  to  the  processes  of  the  posterior  surface  of  the  ciliary  body  as  far  back  as 
the  ora  serrata  of  the  retina.  The  contents  of  the  eyeball  are  under  a  pressure 
which  is  greater  than  atmospheric  by  about  25  cms.  Hg.  They  therefore  press 
outwards  on  the  coats  of  the  eyeball  and  as  a  result  of  this  the  choroid  coat  and 
the  ciliary  body,  its  forward  continuation,  pressed  out  by  the  vitreous  humour, 
pull  backward  as  well  as  outward  on  the  lens  ligament.  This  in  its  turn  exerts 
more  pull  on  the  anterior  than  it  does  on  the  posterior  surface  of  the  lens  capsule. 
The  lens  itself  is  fluid  in  nature  and  its  capsule  is  elastic.  Its  natural  shape  is  a 


Corn-* 


FIG.  43.     Diagram  of  the  attachments  of  the  lens,  and  of  the  neighbouring  structures. 


more  or  less  rounded  one  but,  being  flexible,  it  yields  to  the  pull  of  the  ligament 
and  both  its  surfaces  are  flattened,  the  anterior  however  much  the  more  so. 
The  act  of  accommodation  is  a  contraction  of  the  circular  and  radial  muscle 
fibres  which  are  contained  in  the  ciliary  body.  This  makes  the  circle  of  the 
free  margin  of  the  body  smaller,  brings  it  nearer  to  the  lens,  and  causes  the 
processes  of  the  posterior  part  to  move  forward,  dragging  with  them  the  anterior 
part  of  the  choroid,  with  which  they  are  continuous.  The  fibres  of  the  ligament 


ERRORS  OF  REFRACTION  AND  ACCOMMODATION.  155 

which  pass  between  the  posterior  processes  of  the  body  and  the  anterior  surface 
of  the  lens  are  slackened  by  these  changes  and  the  lens  is  allowed  to  bulge  forward 
by  its  own  elasticity. 

The  extent  to  which  the  curvature  can  be  increased  by  accom- 
modation is  limited  only  by  the  elasticity  of  the  lens. 
Experiment  59. — The  Near  Point. — The  least  distance  at  which 
an  object  may  be  held  away  from  the  eye  and  still  be  clearly 
seen  is  the  NEAR  POINT.  Find  how  far  away  your  own  near 
point  lies  by  looking  fixedly  at  a  pin  or  pencil-point  with  one 
eye  closed  and  gradually  bringing  the  object  closer  to  your  face. 
A  distance  is  found  nearer  than  which  if  the  object  is  held  it  is 
seen  blurred.  The  blurring  means  that  your  accommodation  is 
no  longer  sufficient  to  bring  all  the  rays  from  a  single  point  to  a 
focus  on  the  retina,  the  focus  lies  behind  the  retina,  and  the 
rays  from  each  point  reach  the  sensitive  cells  as  a  pencil,  and 
not  as  a  point  of  light. 

The  near  point  in  a  young  child's  eye  is  generally  about  10  or 
12  cms.  away;  as  time  goes  on  this  distance  increases  and  as  a 
rule  at  40  or  50  years  of  age  the  near  point  has  receded  past  the 
length  at  which  it  is  convenient  to  hold  a  book.  Convex  glasses 
are  then  used  for  reading  and  hand-work  and  by  this  means  the 
divergence  of  the  rays  is  reduced  so  that  objects  may  be  comfort- 
ably held  and  still  throw  sharp  images  on  the  retina.  The  change 
in  elasticity  has  no  effect  on  distant  vision,  the  shape  of  the  lens 
in  the  eye  at  rest  is  the  same  as  before. 

When  the  gaze  is  directed  to  an  object  near  at  hand  two  other 
changes  occur,  associated  with  the  act  of  accommodation.  The 
visual  axes,  which  during  rest  or  distant  vision  are  parallel,  are 
converged  so  that  they  meet  on  the  object  at  which  one  looks,  and 
make  the  image  of  it  fall  on  the  fovea  centralis  of  each  eye.  This  is 
done  by  the  contraction  of  the  internal  recti,  which  rotate  the  eye- 
balls inward.  At  the  same  time  the  ACCOMMODATION  REFLEX  of  the 
pupil  occurs;  the  circular  muscle  fibres  which  are  contained  within 
the  free  margin  of  the  iris  contract  and  reduce  the  size  of  the  open- 
ing. The  iris  acts  as  a  curtain  or  adjustable  diaphragm  for  the 
eye,  limiting  the  size  of  the  pencil  of  rays  which  enter  it.  By  this 
reflex  contraction  of  the  opening  in  near  vision  all  rays  are  shut 
out  except  those  which  pass  through  or  near  the  centre  of  the 


156  EXPERIMENTAL  PHYSIOLOGY. 

refracting  surfaces.  By  this  means  spherical  aberration  is  cut  down 
in  near  vision,  in  which  great  accuracy  is  usually  required  and  in 
which  the  aberration  would  otherwise  be  marked,  because  the 
incoming  rays  are  very  divergent.  The  image  is  made  somewhat 
less  bright  by  this  device,  since  there  are  fewer  rays  to  contribute 
to  it  than  there  would  be  with  a  wider  pupil,  but,  the  object  being 
near,  the  number  of  rays  which  the  eye  receives  from  it  is  in  any 
case  large  and  the  loss  is  not  of  much  importance.  All  three  groups 
of  muscles  which  contract  in  near  vision,  the  ciliary,  the  circular 
muscle  fibres  of  the  iris,  and  the  internal  recti,  are  supplied  by  the 
oculomotor  nerve.  The  nerve  supply  of  the  radial  fibres  of  the 
iris,  the  contraction  of  which  dilates  the  pupil,  comes  from  the 
cervical  sympathetic.* 

Some  indication  of  the  nature  of  the  change  in  the  eye  media 
during  accommodation  may  be  got  from  the  following  experiments. 
Experiment  60. — In  a  dark  room  arrange  the  lens  and  watch  glass 
so  that  they  are  centred,  with  the  lens  behind  the  watch  glass, 
which  is  placed  with  its  convex  side  forward.  Hold  a  candle 
beside  your  head  and  a  little  behind  your  eyes  and  look  at"  the 
images  of  the  flame  formed  by  the  three  refracting  surfaces. 
These  let  most  of  the  light  through,  but  reflect  some  small 
portion  of  it.  The  reflected  rays  form  the  images  which  you 
see.  There  are  three  of  them,  one  inverted  and  two  erect. 
Experiment  61. — Purkinje  Images. — Look  at  your  partner's 
eye  in  the  way  in  which  you  looked  at  the  lens  and  watch  glass 
in  the  last  experiment  and  ask  the  subject  to  gaze  past  you  into 
the  distance, -along  a  line  half  way  between  your  eye  and  the 
candle.  As  before,  three  images  may  be  seen  but  in  this  case 
one  of  the  erect  images  is  larger  and  dimmer  than  the  other. 
Now  ask  the  subject  to  focus  on  your  finger  held  in  his  line  of 
vision,  at  about  the  distance  of  your  head  away.  The  small, 
bright,  erect  image  and  the  inverted  one  are  unchanged  in 
position,  but  the  larger  erect  one  moves  nearer  the  first  and 


*A  stopping-down  of  the  pupil,  similar  to  that  which  occurs  for  near  vision,  is 
brought  about  reflexly  when  the  eye  moves  from  a  darker  to  a  lighter  place.  If 
the  change  in  the  intensity  of  the  light  is  great  the  contraction  is  more  marked  at 
first,  becoming  gradually  less  for  some  minutes  afterwards  as  the  eye  becomes 
'accustomed  to  the  light".  This  is  known  as  the  "LIGHT  REFLEX"  of  the  pupil. 


ERRORS  OF  REFRACTION  AND  ACCOMMODATION.  157 

becomes  smaller  than  before.  This  is  the  image  from  the 
anterior  surface  of  the  lens.  It  is  large  and  dim  in  the  un- 
accommodated eye  because  the  surface  which  forms  it  is  fairly 
flat.  During  accommodation  when  the  surface  becomes  more 
curved  the  image  becomes  smaller  and  appears  to  move  forward 
because  of  the  movement  of  the  reflecting  surface. 
Experiment  62. — Schemer's  Experiment. — The  course  of  rays 
which  enter  the  eye,  from  objects  at  distances  for  which  the 
eye  is  not  accommodated,  can  be  traced  by  blocking  all  but 
two  pencils  of  them  and  finding  out  which  regions  of  the  retina 
are  affected  by  the  two  pencils  of  light.  In  a  piece  of  heavy 
paper  prick  two  holes  less  than  the  diameter  of  the  pupil  apart. 
Stick  two  needles  upright  in  a  strip  of  wood,  one  30  cms.  and 
one  60  cms.  from  the  end.  Hold  the  screen  with  the  holes 
horizontal  in  front  of  one  pupil  and,  closing  the  other  eye, 
look  along  the  stick  and  accommodate  for  the  far  pin.  Note 
that  the  image  of  the  near  pin  is  double.  Cover  one  hole  in 
the  screen  and  see  which  image  disappears.  Repeat,  with  the 
eye  accommodated  for  the  near  pin.  From  your  results  draw 
diagrams  of  the  course  of  rays  entering  the  eye  (a)  from  an 
object  at  the  distance  for  which  the  eye  is  accommodated, 
(b)  from  one  at  a  greater  distance,  (c)  from  one  at  a  less.  Com- 
pare with  the  diagrams  from  the  results  of  Exp.  48  and  explain 
the  differences. 


CHAPTER   XIX. 

EXAMINATION  OF  THE  REFRACTION  OF  THE  EYE  AND 
OF  THE  INTERIOR  OF  THE  EYEBALL. 

THE  OPHTHALMOSCOPE. 

Most  of  the  light  which  enters  the  eye  passes  through  the 
retina  and  is  absorbed  by  the  black  pigment  layer  behind  it  but  a 
small  proportion  of  the  rays  are  reflected  from  the  retina  itself. 
The  rays  reflected  from  each  point  are  refracted  again  by  lens  and 
cornea  being  bent  away  from  the  perpendicular  in  this  case  and  they 
pass  out  in  the  same  general  path  as  was  taken  by  the  incoming  rays 
which  illuminated  the  point.  That  is,  they  travel  back  towards  the 
source  of  light.  Since  the  eye  of  the  observer  is  not  under  ordinary 
circumstances  placed  at  such  a  source  it  does  not  receive  any  of  this 
light  and  therefore  any  pupil  at  which  one  looks  appears  to  be  black. 
If  however  one  arranges  to  have  the  observer's  eye  at  the  source  of 
light,  or  a  very  little  distance  from  it,  some  of  the  rays  reflected  from 
the  observed  retina  can  be  seen. 

This  is  the  principle  on  which  the  ophthalmoscope  is  con- 
structed. It  not  only  gives  a  view  of  the  interior  of  the  eye  but 
also,  as  we  shall  see,  affords  a  method  of  examining  its  refraction. 
The  instrument  is  a  slightly  concave  mirror  with  a  tiny  hole  in  the 
centre  of  it.  One  holds  it  in  front  of  the  eye  which  one  wishes  to 
examine  and  a  light  is  placed  beside  the  eye  and  a  little  behind  it 
(L,  Fig.  44  A.).  The  mirror  sends  rays  from  this  into  the  eye. 
LAA'  and  LBB'  in  Fig.  44  are  two  such  rays.  There  will  of 
course  be  many  others,  lighting  up  the  whole  area  between  A'  and 
B'  and  some  of  them  falling  on  either  side.  Each  point  of  this 
illuminated  area,  reflecting  part  of  the  light  which  it  receives,  acts 
as  a  source  of  rays,  as  -is  shown  for  the  point  X.  The  observer 
looks  from  behind  through  the  little  hole  and  some  of  the  reflected 
rays  (as  XY  and  XZ)  returning  towards  the  mirror  pass  through 
the  hole  and  afford  him  a  view  of  the  interior  of  the  subject's  eye. 

158 


THE  OPHTHALMOSCOPE. 


159 


The  subject  is  asked  to  stare  ahead  of  him,  in  order  to  relax  his 
accommodation,  or,  what  is  more  effective,  an  application  of  atro- 
pine  is  made  to  the  eye.  This  paralyses  the  endings  of  the  third 
nerve  in  the  iris  and  the  ciliary  body  and  prevents  accommodation, 
and  reflex  contraction  of  the  pupil  under  the  stimulus  of  the  strong 
light.  The  rays  from  the  retina,  arising  at  the  principal  focus  if 
the  eye  is  a  normal  one,  pass  out  after  refraction  parallel  to  one 
another.  If  these  are  to  be  clearly  focussed  on  the  observer's 
retina  his  eye  must  be  unaccommodated.  He  must  not  look  there- 


FIG.  44.  To  illustrate  the  use"  of  the  ophthalmoscope.  Upper  diagram  shows  the 
course  of  the  illuminating  rays  and  of  the  outgoing  rays,  by  the  direct  method.  Lower 
diagram  shows  the  course  of  outgoing  rays  when  the  indirect  method  is  used;  the 
illuminating  rays  have  been  omitted. 

fore  at  the  retina  which  he  wishes  to  see  but  must  gaze  through  it 
into  the  distance.  If  the  observed  eye  is  shortsighted,  the  prin- 
cipal plane,  the  plane  from  which  rays  would  have  to  come  to  be  ren- 
dered parallel  after  passing  out  through  lens  and  cornea,  is  some- 
what in  front  of  the  plane  of  the  retina.  Light  rays  from  the 
retina,  therefore,  since  they  diverge  less  than  would  rays  from 
the  principal  plane,  are  too  much  refracted  by  the  eye  media  and 
converge  after  refraction.  If  they  are  to  make  a  sharp  focus  on 
the  unaccommodated  eye  of  the  observer  they  must  be  rendered 


160  EXPERIMENTAL  PHYSIOLOGY. 

parallel  by  a  divergent  lens,  and  the  strength  of  the  lens  which 
one  must  use  for  this  gives  a  measure  of  how  much  the  rays  differed 
in  direction  from  the  parallel  paths  which  they  should  have  taken. 
If  the  eye  is  LONG-SIGHTED  the  condition  is  reversed.  The 
retina  is  farther  forward  than  the  principal  focus  of  the  eye,  the 
rays  diverge  too  sharply  and  after  refraction  they  still  diverge  to 
some  extent.  The  observer  to  see  clearly  must  in  this  case  use  a 
conyergent  lens  and,  as  before,  the  strength  of  the  lens  gives  a  meas- 
ure of  how  different  the  eye  is  from  the  normal.  This  is  known  as 
the  DIRECT  METHOD  of  using  the  ophthalmoscope.  The  part  of  the 
retina  which  one  can  see  at  one  time  in  this  way  is  a  small  one  and 
for  that  reason,  and  sometimes  too  because  it  is  difficult  for  the 
observer,  if  he  is  inexperienced,  to  relax  his  accommodation  com- 
pletely, the  INDIRECT  METHOD  is  often  used  (Fig.  44,  B.).  The 
arrangement  of  light  and  mirror  is  on  the  same  plan  as  before,  but 
in  this  case  a  convex  lens  is  held  immediately  in  front  of  the  subject's 
eye.  This  focusses  the  rays  emerging  parallel  from  the  eye  and 
forms  an  inverted  real  image  of  the  bright  spot  of  the  fundus,  at 
the  principal  focal  plane  of  the  lens.  It  is  this  image  at  which  the 
observer  looks. 

Experiment  63. — The  use  of  the  ophthalmoscope  for  the  examina- 
tion of  the  human  eye  is  not  suitable  as  a  laboratory  experiment 
since  a  beginner  to  have  success  needs  both  time  and  quiet. 
Each  student  is  expected,  however,  at  some  time  during  this 
part  of  the  course,  to  procure  an  instrument,  of  which  there  are 
several  available  in  the  supply  room,  and  to  practise  with  it 
until  he  can  see  for  himself  the  interior  of  a  normal  eye.  Using 
both  the  direct  and  indirect  methods,  work  at  the  experiment 
until  you  can  see  many  or  all  of  the  details  of  the  interior  surface 
of  the  eyeball  described  below  (p.  147).  Before  doing  this  it  is 
wiser  to  practise  a  little  in  the  laboratory,  using  the  instrument 
according  to  both  methods  to  examine  the  eye  of  a  rabbit,  the 
pupil  of  which  has  been  dilated  with  atropine. 
Direct  Method. — Place  the  light  and  ophthalmoscope,  as 
shown  in  Fig.  44,  and  look  from  behind  the  mirror  through 
the  hole.  Start  with  it  about  eighteen  inches  away  from  the 
observed  eye  and  move  it  slowly  about  until  the  pupil  is  seen 
as  a  bright  red  spot.  Now  move  the  mirror  gradually  nearer, 


THE  OPHTHALMOSCOPE. 


161 


keeping  it  always  in  the  same  line,  until  when  you  are  about 
two  or  three  inches  away  from  the  subject's  eye  the  bright  spot 
of  the  retina  comes  clearly  into  view.  Both  observer's  and  sub- 
ject's eyes  must  be  unaccommodated. 

Indirect  Method. — The  arrangement  is  as  before  except  that 
a  converging  lens  is  held  two  or  three  inches  away  from  the 
observed  eye  and  steadied  by  resting  a  finger  of  that  hand 


FIG.  45.  Diagrams  to  illustrate  the  use  of  the  retinoscope.  No.  1  shows  the  path  of  rays 
from  a  normal  eye,  No.  2  that  for  rays  from  a  normal  eye  in  front  of  which  is  held  a  converging  lens, 
or  of  rays  from  a  shortsighted  eye. 

against  the  subject's  forehead.  Hold  the  ophthalmoscope 
about  twenty  inches  away  and  move  it  about  and  move  the 
lens  back  and  forth  until  the  image  of  the  bright  spot  is  clearly 
seen.  The  observer  must  accommodate  his  eye  for  a  point  near 
at  hand. 

THE  RETINOSCOPE.  Another  instrument  which  is  used  to  examine  the 
refraction  in  the  eye  is  the  retinoscope,  a  flat  mirror  with  a  little  peep-hole  in  the 
middle,  which  can  be  made  to  rotate  through  a  small  angle  on  its  handle.  The 
principle  of  its  use  depends  on  the  following  considerations.  If  a  spot  of  light  is 


162  EXPERIMENTAL  PHYSIOLOGY. 

reflected  on  a  wall  and  the  mirror  reflecting  it  is  rotated  upward,  the  movement  of 
the  spot  is  in  the  same  direction  as  that  of  the  mirror.  If  a  spot  of  light  be 
reflected  into  a  normal  eye  and  the  mirror  moved,  the  movement  of  the  light  on 
the  retina  appears  to  the  observer's  eye,  placed  at  the  hole  in  the  instrument,  also 
to  be  in  the  same  direction.  This  is  shown  in  Fig.  45,  No.  1  A  is  the  first 
position  of  the  spot  of  light  and  B  the  second,  moved  by  an  upward  movement  of 
the  mirror.  The  rays  from  A,  when  after  refraction  they  come  out  of  the  eye, 
appear  to  come  from  A'  at  infinity.  Those  arising  from  B  seem  to  come  from  B', 
also  at  infinite  distance.  The  mirror  was  moved  up  and  the  image  also  moves  up. 
If  a  strong  converging  lens  is  held  in  front  of  the  observed  eye  so  that  the  rays 
coming  out  are  made  to  form  inverted  images,  at  some  short  distance  from  the 
lens,  of  the  retinal  points  from  which  they  arise,  and  if  the  rays  are  diverging  from 
the  images  again  when  they  reach  the  observer's  eye,  the  condition  is  reversed. 
The  spot  of  light  appears  to  move  in  a  direction  opposite  to  that  of  the  movement 
of  the  mirror.  This  is  shown  in  Fig.  45,  No.  2.  The  rays  from  A,  converged  after 
coming  out  of  the  eye,  make  the  image  at  A',  those  from  B  at  B'.  If  the  observer's 
eye  be  farther  away  than  A' and  B',  the  rays  from  the  first  (lower)  position  of  the 
spot  of  light  seem  to  come  from  the  upper  image,  those  from  the  second  place  of 
the  spot,  which  was  really  above  the  first,  from  an  image  lower  than  the  first  image. 
The  direction  of  movement  is  thus  reversed.  If  the  observer's  eye  be  nearer  than 
the  focus  of  the  lens  (that  is,  nearer  than  A'  or  B'),  the  movement  appears  to  be 
in  the  direction  of  the  movement  of  the  mirror,  as  it  was  without  the  lens.  Sup- 
pose the  observer's  eye  is  always  at  a  distance  of  one  metre  from  the  subject. 
Then  if  the  lens  is  stronger  than  one  dioptre  (i.e.,  has  a  focal  length  of  less  than 
one  metre)  the  spot  will  move  in  the  opposite  direction.  If  the  lens  is  weaker  than 
this  there  will  be  no  reversal,  and  the  spot  will  move  in  the  same  direction  as  the 
mirror.  Now,  if  the  subject's  eye  is  not  normal  but  long-sighted,  the  rays  when 
they  come  out  diverge  from  each  other.  To  bring  these  to  a  focus  in  front  of  his 
eye,  still  at  one  metre  distance,  the  observer  will  have  to  use  a  stronger  lens  than 
before  and  the  more  long-sighted  the  eye  is,  the  stronger  the  lens  will  have  to  be. 
Rays  coming  from  a  short-sighted  eye  are  already  converging  when  they  come  out. 
If  the  defect  is  small,  a  converging  lens  will  still  be  needed  to  make  the  movement 
of  the  spot  appear  reversed  to  an  observer  at  one  metre,  though  not  so  strong  a  one 
as  is  needed  for  the  normal  eye.  If  the  defect  is  great,  the  focus  of  the  rays 
without  any  lens  at  all  may  lie  at  some  point  between  observer  and  subject,  and 
in  this  case  the  spot  of  light  moves  in  the  opposite  direction  to  the  mirror  from 
the  first.  The  condition  will  be  thus  like  that  already  described  for  Fig.  45, 
No.  2,  only  that  no  lens  need  be  imagined.  A  divergent  lens  must  be  used  to 
cause  it  to  go  to  the  similar  direction  and,  as  before,  the  strength  of  the  lens  which 
must  be  used  gives  a  measure  of  the  abnormality.  An  examination  of  this  kind 
can  be  done  in  any  plane  of  the  eye  and  the  method  can  therefore  be  used  to 
measure  astigmatism.  In  this  case  the  strength  of  lens  necessary  to  give  reversal 
when  one  plane  of  movement  is  being  tested  is  different  from  that  for  another 
plane. 


CHAPTER   XX. 

THE  RETINA. 

The  view  of  the  interior  of  the  eyeball  which  one  gets  with  an 
ophthalmoscope  reveals  a  whitish  lining,  the  retina,  over  thejsurface 
of  which  are  fine  branches  of  arteries  which  supply  it  with  blood. 
There  are  two  spots  on  it  which  differ  in  their  appearance  from  the 
rest  of  the  surface.  One  of  these,  situated  directly  opposite  the 
centre  of  the  pupil,  is  the  MACULA  LUTEA.  This  is  slightly  raised, 
yellowish  in  colour,  and  has  a  tiny  depression  in  its  centre,  the 
FOVEA  CENTRALIS,  the  part  of  the  retina  capable  of  the  most  accurate 
vision.  The  blood  vessels  skirt  around  the  yellow  spot  and  do  not 
pass  across  it.  Towards  the  nasal  side  of  this  and  some  little 
distance  from  it  there  is  a  shining  white  spot,  the  OPTIC  DISC,  which 
marks  the  passage  through  the  retina  of  the  fibres  of  the  optic 
nerve. 

In  order  that  the  student  may  have  the  structure  of  the  retina  fresh  in  his 
mind  as  a  basis  for  his  experiments,  he  is  reminded  of  the  details  of  its  anatomy 
and  histology  which  follow. 

The  fibres  of  the  optic  nerve  enter  the  eyeball  from  outside  arranged  in  a 
cylindrical  fashion,  enclosing  in  the  middle  an  artery,  branches  of  which  we  have 
seen  ramifying  over  the  surface  of  the  retina.  When  they  have  pierced  the  outer 
layers  of  the  retina,  the  nerve  fibres  of  the  cylinder  divide  and  spread  out  over  its 
whole  surface,  thus  forming  the  innermost  retinal  layer  of  all.  The  whole  retina 
extends  forward  in  the  eyeball  only  as  far  as  the  beginning  of  the  ciliary  processes. 
From  here  on  it  is  represented  simply  by  the  layer  of  black  pigment  cells  which 
clothes  the  posterior  surface  of  the  ciliary  body.  The  cells  which  are  sensitive  to 
light  waves,  the  fundamental  part  of  the  whole  organ  of  vision,  are  contained  in  one 
of  the  layers  of  the  retina.  The  retina  itself  is  to  be  regarded  not  simply  as  com- 
parable to  a  group  of  sensory  nerve  endings,  connected  each  by  a  single  fibre 
directly  to  the  central  nervous  system,  but  as  a  part  of  the  brain  itself,  from  an 
outgrowth  of  which  it  is  formed  during  the  development  of  the  foetus.  Accord- 
ingly it  contains,  as  well  as  the  light-sensitive  cells  themselves,  two  layers  of  relay 
cells  through  which  the  impulses  arising  in  the  sensitive  elements  must  pass  on 
their  way  to  the  brain  (Fig.  46).  The  elements  which  respond  to  light  waves,  the 
rods  and  cones,  are  placed  farthest  away  from  all  the  incoming  light.  They 
are  the  free  ends  of  the  outer  cell  layer,  sticking  out  towards  the  choroid  coat  from 
which  they  are  separated  only  by  a  layer  of  black  pigment  cells.  The  nuclei 

163 


164  EXPERIMENTAL  PHYSIOLOGY. 

corresponding  to  them  are  nearer  the  centre  of  the  eyeball  and  each  cell  sends  a 
connecting  fibre  inward  into  the  outer  nuclear  layer  of  the  retina,  where  it  is  con- 
nected with  the  dendrites  of  one  of  the  first  relay  cells,  the  bipolar  cells.  The  rods 
have  slightly  thickened  inner,  and  straight  slender  outer,  limbs.  They  are  con- 
nected with  their  nuclei  by  fine  thread-like  processes.  The  cones,  which  are 
shorter  than  the  rods,  are  also  divided  into  inner  and  outer  limbs.  Their  outer 
limbs  are  shorter  and  sharper  than  those  of  the  rods;  the  inner  ones  are  much 
thicker  and  connected  each  by  a  substantial  process  with  its  nucleus,  which  lies 
nearer  to  it  than  do  those  of  the  rods.  The  dendrites  of  the  bipolar  cells,  which  are 
the  next  units  on  the  path  of  the  impulse,  are  connected  by  short  thick  processes 
with  their  cell  bodies,  the  nuclei  of  which  make  up  the  inner  nuclear  layer. 
The  axones  of  these  cells  are  short.  They  end  in  the  inner  molecular  layer, 
where  they  establish  connection  with  the  dendrites  of  the  second  relay  cells,  the 
giant  cells.  It  is  the  axones  of  the  giant  cells  which,  passing  over  the  surface, 
make  the  inner  layer  of  the  retina  and  join  together  at  the  optic  disc  to  go  out  as 
the  optic  nerve.  In  all  parts  of  the  retina  except  the  fovea  centralis  the  bipolar 
cells  connect  each  with  several  fibres  from  rod-cells  or  ccne-cells,  and  are  in  turn 


FIG.  46.     Diagram  of  the  structures  in  the  retina. 

several  of  them  connected  with  one  giant  cell,  so  that  the  number  of  nerve  elements 
represented  in  the  optic  nerve  is  a  good  deal  less  than  the  number  of  cells  in  the 
retina,  and  one  fibre  in  the  nerve  may  carry  impulses  which  arise  from  any  one  or 
from  all  of  a  number  of  rods  or  of  cones.  The  histology  of  the  fovea  is  different 
in  this  as  in  some  other  respects  from  that  which  we  have  described.  It  consists 
only  of  the  light-sensitive  cells  and  the  fibres  which  connect  them  with  the  first 
relay  cells.  These,  together  with  the  giant  cells  to  which  they  lead,  are  swept 
aside  from  the  fovea  itself  and,  piled  up  around  its  margin,  cause  the  slight 
thickening  of  the  retina  which  surrounds  it.  The  sensitive  cells  in  the  fovea 
are  all  cones,  no  rods  are  to  be  found,  and  they  are  each  of  them  connected  through 
a  different  bipolar  cell  to  a  single  giant  cell  and  so  to  a  separate  fibre  of  the  optic 
nerve.  The  arrangement  affords  some  histological  basis  for  the  acuteness  of 
vision  which  we  have  in  the  fovea,  since  each  cone  has  a  separate  path  to  the  brain. 
It  is  found  that  two  points  in  the  external  world  may  be  distinguished  as  separate, 
provided  that  the  angle  by  which  they  are  separated  at  the  eye  is  5  minutes  or 


THE  RETINA.  165 

more,  and  provided  that  they  are  looked  at  directly,  that  is,  that  their  image 
falls  on  the  fovea.  Construction  by  the  schematic  eye  shows  that  an  angle 
of  this  size  represents  an  image  of  about  .0035  mm.  on  the  retina,  approximately 
the  distance  from  the  centre  of  one  cone  to  that  of  another.  If  the  points  are 
looked  at,  not  directly,  but  with  'the  tail  of  one's  eye',  they  must  be  much  more 
widely  separated  than  this  to  appear  distince  from  each  other;  the  distance 
necessary  increases,  broadly  speaking,  the  farther  they  are  removed  towards  the 
periphery  of  the  visual  field. 

That  the  cells  which  are  most  deeply  placed  of  all  should  be 
those  which  respond  to  the  vibrations  of  the  light  waves  would  at 
first  sight  appear  improbable.     There  is  abundant  evidence,  how- 
ever, that  this  is  the  case,  as  the  two  following  experiments  show. 
Purkinje  Figures. — The  retinal  blood  vessels,  being  situated 
between  the  source  of  light  and  the  receptive  surface  cast  shadows 
on  the  retina.    These  are  very  small  and  by  habit  are  disregarded. 
If,  however,  they  can  be  made  to  fall  on  some  part  of  the  retina 
which  ordinarily  does  not  receive  them  they  may  be  seen. 
Experiment  64. — Make  the  subject  turn  one  eye  inward  and  look 
towards  a  dark  wall.    With  a  lens  concentrate  a  good  light  upon 
the  exposed  sclerotic,  focussing  so  as  to  make  a  small,  strongly 
illuminated  area.    Now  give  the  lens  a  circular  or  gently  rocking 
motion.    The  field  appears  to  the  subject  to  be  reddish  yellow, 
with  dark  branching  figures  on  it.     These  are  the  shadows  of 
blood  vessels.    In  the  direct  line  of  vision  a  small  spot  free  from 
shadows  may  be  seen,  the  macula  lutea  or  yellow  spot. 
The  path  of  the  light  rays  through  sclerotic  and  choroid  and 
the  vitreous  humour  is  shown  in  the   diagram  (Fig.   47).     When 
the  source  of  light  is  moved  there  is  a  movement  of  the  shadow  of 
the  blood  vessel  on  the  retina,  which  is  projected  outward  by  the 
subject  along  the  line  which  connects  the  point  stimulated  with  the 
nodal  point,  and  which  is  interpreted  as  a  movement  of  a  shadow  in 
the  field  of  vision  at  the  distance  for  which  the  eye  is  accommodated. 
A  is  the  first  position  of  the  light,  A'  the  place  on  the  retina  where 
it  throws  the  shadow,  A"  the  place  on  the  screen  at  which  the  eye 
appears  to  see  the  shadow.     When  the  light  is  moved  to  B  the 
shadow  moves  to  B'  and  its  apparent  place  in  the  field  to  B". 
n.p.  is  the  nodal  point  of  the  eye,  b.v.  the  position  of  the  blood 
vessel.     Now  triangles  A"B"  n.p.  and  n.p.A'B'  are  similar  and  we 
know  the  lengths  A"B",  n.p.A"  and  n.p.A'.    We  can  therefore  find 


166 


EXPERIMENTAL  PHYSIOLOGY. 


A'B',  the  distance  the  shadow  actually  moved  on  the  retina.  But 
triangles  A'B'  b.v.  and  bv.AB  are  also  similar.  Here  we  know 
A'B',  A.B.  and  (approximately)  bvA.,  so  that  we  can  find  bv.A', 
the  distance  between  light-sensitive  layer  and  the  blood  vessel. 
This  is  found  to  be  about  0.2-0.3  mm.,  which  is  sufficiently  like  the 
distance  actually  existing  between  the  retinal  blood  vessels  and  the 
layer  of  rods  and  cones  to  support  the  conclusion  that  these  are 
the  elements  sensitive  to  light. 


FIG.  47.  To  illustrate  the  course  of  the  rays  w  hich  cast  the  shadows  in  Purkinje's 
figures,  and  the  direction  along  which  these  shadows  are  projected  outward  into  the 
visual  field. 


Blind  Spot. — It  may  easily  be  shown  that,  although  we  are 
unconscious  of  it,  there  is  an  area  in  the  field  of  vision  of  each  eye 
which  is  blank;  objects  placed  there  are  not  seen.  Construction 
with  the  schematic  eye  shows  that  light  rays  from  this  area  fall  on 
the  optic  disc.  Here,  as  we  have  seen,  there  are  no  rods  or  cones, 
the  layers  which  contain  them  being  interrupted  to  allow  of  the 
passage  through  it  of  the  fibres  of  the  optic  nerve. 


THE  RETINA.  167 

Experiment  65. — Take  a  thin  strip  of  paper  and  blacken  about 
1  mm.  of  its  end.  Hold  a  large  sheet  of  paper  with  a  dot  in 
the  centre  vertically  in  front  of  you.  Keeping  your  head  quite 
still,  close  one  eye  and  look  fixedly  at  the  dot  with  the  other. 
Move  the  blackened  end  of  the  paper  strip  slowly  over  the  field 
of  vision  and  mark  the  points  when  it  seems  to  disappear. 
From  these  points  map  out  the  area  of  the  blind  spot  in  the 
visual  field.  Using  the  schematic  eye,  show  where  it  must  be 
in  the  retina. 

The  Response  of  the  Retina  to  Light.— In  addition  to  the 
information  from  subjective  experiments  such  as  those  which  we 
are  about  to  discuss,  which  of  course  involve  activity  of  the  brain 
as  well  as  the  eye,  some  interesting  knowledge  as  to  the  nature  of 
the  retina's  reaction  to  light  stimuli  has  been  got  from  direct 
experiments  on  the  eye  itself.  The  technique  which  shows  the 
movement  of  the  cones,  the  negative  variation  in  the  retina,  and 
the  formation  and  destruction  of  the  visual  purple,  is  unfortunately 
too  difficult  for  class  experiments.  The  student  must  turn  to  his 
text-books  for  information  as  to  the  nature  and  significance  of  this 
work. 

DARK  ADAPTATION. — It  is  familiar  that  eyes  at  night  or  in  a  dark  room  can  see 
lights  so  faint  that  they  would  not  be  made  out  at  all  by  day.  This  is  in  part  due 
to  an  actual  lowering  of  the  threshold  of  the  light-sensitive  elements,  and  one  may 
satisfy  oneself  by  simple  experiments  that  the  main  part  at  least  of  this  change 
in  threshold  occurs,  not  in  the  line  of  direct  vision,  but  in  the  peripheral  field. 
The  observations  are  entirely  subjective  ones  and  the  student  must  make  them 
for  himself  under  suitable  conditions  of  lighting.  If  one  looks  at  the  sky  at  twi- 
light searching  for  the  first  star  it  may  appear  on  one  side  or  another  of  the  direct 
line  of  vision,  only  to  disappear  when  looked  at  directly.  Small  pieces  of  white 
paper  on  a  black  background  in  a  darkened  room  are  visible  as  long  as  they  are 
not  in  the  direct  line  of  vision,  but  disappear,  each  as  its  image  is  made  to  fall  on 
the  fovea.  Indeed,  workers  in  this  field  have  not  been  able  to  find  that  any 
lowering  of  the  threshold  at  all  occurs  in  the  fovea  during  adaptation  to  the  dark 
and  this  makes  it  probable  that  the  change  in  the  threshold  of  the  peripheral 
field  is  a  change  in  the  rods  and  is  not  shared  by  the  cones.  The  adaptation 
which  the  rods  undergo  is  thought  to  be  associated  with  the  presence  in  them 
of  visual  purple,  the  coloured  substance  which  is  formed  in  them  in  the  dark. 
One  of  the  chief  reasons  for  this  is  the  striking  resemblance  between  the  sen- 
sitiveness of  the  pigment  on  one  hand,  and  of  the  dark-adapted  eye  on  the 
other,  to  waves  of  different  lengths.  When  several  different  colours  are  seen 
under  similar  lighting  conditions  it  is  only  a  matter  of  judgment  which  of  them  is 


168  EXPERIMENTAL  PHYSIOLOGY. 

the  brightest,  but  most  normal  individuals  if  shown  a  spectrum  in  a  brightly 
lighted  room,  pick  out  the  yellow  as  the  brightest  part  of  it,  brighter  than  either 
red,  orange,  green,  blue  or  violet.  If  however  all  light  is  shut  out  of  the  room 
except  that  coming  through  the  prism  which  makes  the  spectrum,  and  if  the  eyes 
are  allowed  to  become  adapted  to  the  dark,  the  place  of  greatest  brightness  in  the 
spectrum  appears  to  shift  from  yellow  to  green.  This  colour,  it  is  to  be  noted,  is 
also  the  most  effective  in  bleaching  the  visual  purple.  The  spectrum  under  these 
conditions  also  appears  shortened  at  the  red  end,  that  is  to  say  the  long  waves  are 
ineffective  for  the  eyes  in  this  state,  as  they  are  also  found  to  be  on  the  purple 
itself. 

Some  further  evidence  which  bears  on  the  same  question  is  got  from  obser- 
vations on  the  ACHROMATIC  (or  colourless)  THRESHOLD.  If,  after  the  eyes  have 
become  adapted  to  a  dark  room,  light  is  gradually  introduced,  all  objects  in  the 
room  of  any  colour  except  red  look  colourless  when  first  they  become  perceptible, 
as  if  they  were  made  up  of  varying  shades  of  white  and  grey,  and  it  is  only  on 
farther  illumination  that  they  appear  in  their  own  tints.  The  interval  during 
which  they  seem  uncoloured  is  the  achromatic  interval.  Red  objects  have  no 
such  interval;  they  appear  at  once  in  their  own  colour,  but  they  require  a  stronger 
light  to  make  them  visible  than  is  needed  to  make  the  other  objects  show  as 
colourless  grey  ones.  The  whole  phenomenon  can  be  seen  out  of  doors  at  dawn, 
or,  in  the  reverse  order,  at  dusk.  At  the  first  daylight  everything  comes  into 
view  as  if  in  a  print,  all  black,  white  or  grey,  and  it  is  only  as  the  light  increases 
that  the  leaves  change  from  grey  to  green,  blues,  yellows  and  violets  appear,  and 
red  flowers  turn  from  black  objects  to  brightly  coloured  ones.  These  results  are 
interpreted  as  follows :  in  the  light  the  cones  have  a  threshold  lower  than  that  of  the 
rods  and,  since  they  are  capable  of  distinguishing  colours  as  well  as  merely  bright- 
ness, we  see  all  light  in  which  there  is  more  of  some  wave  lengths  than  of  others  as 
coloured  light,  no  matter  how  faint  it  may  be.  In  the  dark  adapted  eye  the 
threshold  of  the  cones  is  not  changed,  but  that  of  the  rods  is  lowered,  probably 
because  of  the  presence  in  them  of  the  visual  purple,  so  that  they  become  more 
sensitive  than  the  cones.  The  rods  are  not  organs  of  colour  vision,  however, 
when  stimulated  they  give  rise  only  to  sensations  of  brightness.  Therefore  faint 
lights  of  wave  lengths  other  than  red  are  first  seen  by  the  rods  of  the  dark-adapted 
eye  as  colourless  rays  and  only  affect  the  cones  and  appear  coloured  when  they 
have  become  a  good  deal  stronger.  Red  lights  do  not  affect  the  rods  at  all,  and 
their  effect  does  not  appear  until  they  are  strong  enough  to  stimulate  the  cones. 

There  is  an  abnormal  type  of  vision  known  as  TOTAL  COLOUR  BLINDNESS, 
which  shows  a  good  many  points  or  resemblance  to  the  vision  of  a  dark-adapted 
eye.  People  who  have  this  defect  see,  as  far  as  one  can  determine,  all  lights  as 
colourless;  rays  of  different  wave-lengths  differ  to  them  only  in  brightness  and 
any  two  colours  can  be  made  to  look  exactly  alike  to  the  colour  blind  by  varying 
the  brightness  of  one  or  the  other.  Two  colours  which  match  in  their  judgment 
look  equally  bright  also  to  the  normal  eye  in  its  condition  of  dark  adaptation,  but 
are  different  not  only  in  colour  but  in  brightness  under  ordinary  conditions  of 
lighting.  Like  the  dark  adapted  eye  the  colour-blind  is  more  sensitive  to  the 


THE  RETINA.  169 

shorter  wave  lengths;  a  green  which  appears  to  the  colour-blind  eye  to  match  a 
certain  yellow  seems  to  the  normal  in  daylight  to  be  not  only  of  a  different  colour 
from  the  yellow  chosen,  but  also  less  bright  than  it.  The  sight  of  people  who  have 
this  defect  is  easily  fatigued  in  bright  light  and  is  much  less  acute  than  the  normal. 
In  the  dark  it  far  surpasses  the  normal  in  accuracy.  Many  colour-blind  people 
have  a  blind  spot  in  the  fovea,  so  that  they  see  nothing  in  the  direct  line  of  vision 
but  only  in  the  peripheral  field.  It  is  thought  that  the  condition  is  one  in  which 
the  rods  mainly  function.  The  parallel  between  these  eyes  and  the  normal  dark- 
adapted  eyes  is  not  complete.  The  vision  of  the  colour-blind  is  much  the 
more  acute  and  is  often  enough  so  to  enable  the  subjects  to  read,  which  cannot 
be  done  with  normal  dark-adapted  eyes. 


CHAPTER   XXI. 

COLOUR  VISION. 

It  is  a  familiar  fact  that  when  ordinary  white  light  is  passed 
through  a  prism  the  waves  of  which  it  is  composed  are  refracted 
to  a  greater  or  less  extent  according  to  their  length.  As  a  result 
the  single  beam  which  was  made  up  of  waves  of  all  lengths  is  spread 
out  into  a  band  of  light,  one  end  of  which  is  formed  by  the  shortest 
of  all  the  visible  rays,  the  part  immediately  next  to  it  by  those  a 
little  longer,  and  so  on  throughout  the  whole  band  until  the  other 
end  is  reached,  which  contains  the  longest  waves  that  the  eye  can 
perceive  as  light.  The  physiological  effect  of  this  re-arrangement 
of  the  waves  is  to  make  the  light,  which  when  mixed  was  uncoloured 
or  white,  appear  to  be  made  up  of  a  whole  series  of  colours,  known 
as  the  spectrum.  The  colours  are  arranged  in  a  definite  order 
according  to  the  length  of  the  waves  of  each  part  of  the  band  of 
light.  The  shortest  of  all  look  violet,  those  next  them  blue,  the 
waves  next  these  again  green,  then  yellow,  then  orange,  and  then 
red,  first  scarlet  and  then,  at  the  end  of  the  band,  crimson.  Each 
colour  shades  inperceptibly  into  the  one  next  it,  so  that  as  well  as 
those  which  we  have  mentioned  we  can  find  in  the  spectrum 
numbers  of  others,  such  as  greenish-blue,  violet-blue,  greenish- 
yellow,  and  so  on.* 

There  are  two  other  ways  in  which  lights  may  differ  from  one 
another.     One  is  in  BRIGHTNESS.     Of  two  rays  of  the  same  colour 
if  one  is  more  intense  than  the  other  it  looks  brighter. 
Experiment  66. — Take  two  sheets  of  paper  of  the  same  colour. 

Place  one  near  an  electric  light  of  low,  and  the  other  near  a  light  of 

high,  candle-power.     The  second  looks  brighter  than  the  first. 

*Each  of  the  spectral  colours  may  also  be  produced  by  the  use  of  pigments. 
The  colours  of  these  depend  on  the  fact  that,  from  the  waves  of  different  lengths 
in  a  beam  of  white  light  falling  on  them,  they  absorb  all  except  those  which 
belong  to  a  very  limited  area  of  the  spectrum.  Blue  paint,  for  instance,  reflects 
only  the  blue  waves  and  a  few  of  the  green  and  absorbs  all  the  others.  Yellow 
glass  absorbs  most  of  the  wave  lengths  falling  on  it  except  the  yellow  ones,  and 
light  which  has  passed  through  it  consequently  has  that  colour. 

170 


COLOUR  VISION.  171 

The  other  way  in  which  two  samples  of  the  same  colour  may 
differ  is  in  the  proportion  of  white  light  which  they  contain.  A 
colour  which  contains  no  white  light  at  all  is,  physically  speaking, 
completely  SATURATED  or  full;  the  more  white  one  mixes  with  it 
the  less  saturated,  or  the  paler,  it  becomes. 

Experiment  67. — Take  two  sheets  of  yellow  tissue  paper  and  put 
one  over  a  piece  of  heavy  paper  of  the  same  shade  and  lay 
the  other  over  a  sheet  of  white  paper.  They  both  have  the  same 
colour  but  the  first  is  fuller  or  more  saturated  than  the  second, 
.paler  one. 

The  evidence  which  we  have  examined  so  far  would  lead  one 

to  think  that  the  sensation  of  a  given  colour  was  entirely  dependent 

on  the  action  on  the  retina  of  waves  of  a  certain  length.    It  would 

seem  that  the  sensation  of  yellow,  for  instance,  was  simply  the 

physiological  result  of  the  action  of  waves  from  that  particular  part 

of  the  spectrum.     The  student's  attention  however  is  directed  in 

this  regard  to  the  results  of  the  two  following  experiments. 

Experiment  68.— The  Effect  of  Stimulating  the  Retina  with 

Two  Different  Colours  at  the  Same  Time. — From  the  paper 

discs     provided    choose    an     orange    and     a    green,    colours 

situated  immediately  on  either  side  of  yellow  in  the  spectrum, 

the  waves  of  one  being  longer  and  those  of  the  other  shorter 

than  the  yellow  waves.     Arrange  them  in  the  rotator  so  that 

about  half  of  each  shows  and  spin  them  rapidly  until  they  seem 

to  fuse.*     The  colour  which  together  they  produce  is  a  yellow 


*The  ideal  way  to  mix  colours  on  the  retina  is  to  cause  the  rays  from  those 
parts  of  the  spectrum  which  contain  the  desired  colours  to  converge  again,  so  that 
they  actually  fall  on  the  retina  at  the  same  time.  A  simpler  means  is  that  adopted 
here,  in  stimulating  the  retina  with  alternate  flashes  of  the  colours  following  each 
other  in  very  rapid  succession.  Advantage  is  taken  of  the  fact  that  the  reaction 
of  the  retina  does  not  cease  immediately  the  stimulus  is  withdrawn  but  lasts  for  a 
fraction  of  a  second  after  it.  The  result  cannot  be  got  by  mixing  together  pig- 
ments of  the  colours  which  it  is  desired  to  combine.  For  instance,  although  blue 
and  yellow  light  thrown  together  on  the  retina  give  white  or  grey,  blue  and  yellow 
pigments  mixed  give  a  green  colour.  The  reason  for  this  is  that  both  blue  pigment 
and  yellow  pigment  reflect,  along  with  their  particular  colours,  some  green  rays. 
When  they  are  mixed  the  blue  absorbs  yellow  light  which  the  yellow  pigment 
would  have  reflected,  the  yellow  pigment  does  as  much  for  the  blue,  and  the  only 
colour  left  over  is  the  green,  which  was  completely  absorbed  by  neither. 


172  EXPERIMENTAL  PHYSIOLOGY. 

much  like  the  pure  spectral  colour,  only  a  little  less  saturated. 
Change  the  disks,  taking  this  time  reddish-orange  and  yellowish- 
green.  These  colours  are  also  one  of  longer  and  one  of  shorter 
wave  length  than  yellow  but  they  are  more  widely  separated 
from  it  in  the  spectrum  than  the  first  two  were.  When  you  spin 
them  you  again  get  a  yellow  but  this  time  there  is  a  much 
greater  proportion  of  white  in  it,  it  is  less  saturated  than  before. 
Replace  these  colours  with  two  others  still  further  removed 
from  yellow,  although  still  lying  one  on  either  side  of  it;  use 
scarlet  and  blue-green.  When  spun  together  this  combination 
looks  whitish  or  pure  grey,  the  yellow  is  no  longer  produced. 
Two  colours  such  as  these,  which  give  a  sensation  of  colourless 
or  white  light  when  combined  on  the  retina,  are  COMPLEMEN- 
TARY COLOURS.  There  are  innumerable  such  pairs,  a  few  of 
them  being  the  following;  orange  with  blue,  bright  yellow  with 
a  more  violet  blue,  green-yellow  with  violet.  Try  these  for 
yourself.  It  may  be  necessary  to  show  in  each  case  a  little 
more  of  one  of  the  pair  than  of  the  other,  depending  on  whether 
or  not  they  are  equally  bright.  In  experimenting  on  these 
complementary  colours  notice  that  when  they  are  arranged  in 
any  proportion  other  than  that  which  gives  white,  they  produce 
a  sensation  of  some  colour  which  lies  between  them  in  the 
spectrum,  just  as  those  pairs  did  which  were  less  widely  sepa- 
rated. 

Now  take  pairs  of  colours  too  widely  separated  to  be  com- 
plementary, for  instance  red  and  blue,  or  orange  and  violet, 
and  see  that  combining  them  gives  a  sensation  of  purple,  a 
colour  which  does  not  exist  in  the  spectrum  at  all.  It  is  the 
complementary  colour  to  green. 

We  have  seen  that  a  colour  sensation,  yellow  for  instance,  can  be 
produced  (a)  by  waves,  acting  alone,  of  the  length  of  those  which 
make  up  the  yellow  part  of  the  spectrum,  or  (b)  by  a  great  many 
combinations  in  pairs  of  waves  of  other  lengths,  waves  which 
falling  alone  on  the  retina  give  colours  which  have  no  yellow  in 
them  at  all.  We  have  also  seen  that  two  beams  of  different  wave 
lengths,  as  well  as  producing  each  a  definite  colour  sensation  when 
it  acts  alone,  can  if  combined  in  varying  proportions  give  rise  to 
quite  a  large  number  of  the  other  colours.  ALL  the  colours,  how- 


COLOUR  VISION. 


173 


ever,  can  not  be  got  by  using  any  one  pair;  to  get  the  whole  range 
of  possible  colour  sensations  you  must  take  at  least  three  spectral 
colours  and  vary  these.     There  are  many  combinations  of  three 
which  can  be  taken,  we  have  chosen  those  most  generally  used. 
Experiment   69, — Effect    of    Simultaneous    Action    on    the 
Retina  of  Three  Primary  Colours. — Put  into  the  rotator  a 
red,  a  green,  and  a  violet  disk.     Keep  on  altering  the  propor- 
tions of  each  until  you  have  got  (a)  a  colourless  light,  (b)  each 
of  the  colours  of  the  spectrum  and  (c)  a  purple. 
As  you  have  seen,  all  the  various  colour  sensations  which  we 
are  capable  of  receiving  can  be  produced  by  combined  action  on 
the  retina  of  three  simple  stimuli.    To  put  the  matter  differently, 
the  whole  range  of  the  response  of  the  retina  to  light  can  be  ex- 
pressed as  a  function  of  three  independent  variables. 


R. 


ft         O  C^  -B          V- 

FIG.  48.     To  illustrate  the  Young  theory  of  colour  vision. 


y 


YOUNG-HELMHOLTZ  THEORY  OF  COLOUR  VISION. — 'Any  theory  which  is  to  be 
advanced  in  explanation  of  colour  vision  must  be  based  on  the  fundamental  facts 
which  we  have  just  described.  The  earliest  of  the  modern  theories,  and  one 
which  has  given  rise  to  a  great  deal  of  experimental  work,  was  first  suggested  by 
Young  and  later  elaborated  by  Helmholtz.  According  to  this  there  are  three 
different  components  in  the  retina,  whether  anatomical  units,  or  chemical  sub- 
stances, is  not  stated.  Each  of  these  is  supposed  to  be  most  effectively  acted 
upon  by  light  waves  of  a  quite  limited  part  of  the  spectrum,  and  those  waves 
which  influence  one  of  the  substances  most  have  very  little  effect  on  either  of  the 
other  two.  For  the  sake  of  illustration,  red,  green  and  violet,  were  selected 
as  the  'primary  colours.'  One  component  is  supposed  to  be  sensitive  to  red 
waves,  less  so  to  orange  and  responsive  in  a  gradually  decreasing  degree  to  the  rest 
of  the  spectrum.  The  green  component  is  affected  most  by  green,  to  a  less  extent 
by  yellow  or  blue,  and  little  by  the  colours  at  either  end.  The  third  component, 


174  EXPERIMENTAL  PHYSIOLOGY. 

as  well  as  responding  to  violet,  is  sensitive  to  blue,  but  little  to  the  other  wave 
lengths  (Fig.  48).  If  any  one  of  these  components  is  stimulated  much  more 
than  the  others  the  result  is  a  sensation  of  the  primary  colour  corresponding  to  it. 
Sensations  of  colours  which  lie  intermediate  to  the  primary  colours  in  the  spectrum 
are  simply  the  result  of  less  unequal  stimulation  of  two  of  the  primary  substances; 
that  explains  why  you  can  get  such  a  sensation  either  by  using  a  wave  length  (such 
as  blue)  which  affects  two  components  (violet  and  green),  one  more  than  the 
other,  or  by  stimulating  the  retina  with  waves  of  two  other  colours  (violet  and 
green)  but  unequal  intensities,  one  of  which  stimulates  mainly  one,  and  one 
mainly  the  other,  of  the  same  components.  If  any  two  components  are  stimulated 
equally  a  sensation  of  white  light  results;  complementary  colours  are  therefore 
merely  those  which  have  an  equal  effect  on  two  of  the  components.  Whether 
or  not  a  colour  is  more  or  less  saturated  depends  on  whether  the  components  other 
than  the  one  mainly  involved  are  responding  much  to  the  light  or  not. 

Experiment  70. — After  Images. — Look  fixedly  for  a  few  seconds 
at  a  bright  object  (the  filament  of  an  electric  light  will  do)  and 
then  transfer  your  gaze  to  a  black  background.  The  bright 
image  does  not  disappear  at  once  but  only  fades  gradually 
away.  This  is  a  POSITIVE  -AFTER-IMAGE.  Repeat,  after  the 
image  has  quite  faded,  but  this  time  move  your  eyes  to  a  brilli- 
antly lighted  white  background.  There  is  a  persistent  image 
in  this  case  also,  of  the  same  shape  as  the  object,  but  whereas 
the  object  was  a  bright  one  the  image  looks  dark.  This  is  a 

NEGATIVE   AFTER-IMAGE. 

Look  steadily  at  a  tiny  spot  in  the  centre  of  a  square  of 
bright  red  paper,  well  lighted.  After  a  few  minutes  shift  the  gaze 
to  a  white  background.  You  see  the  square  still,  but  tinged 
with  greenish-blue,  the  colour  complementary  to  red.  Repeat, 
after  waiting  until  the  after-image  has  faded,  with  a  yellow 
square,  then  try  with  a  green  one.  The  negative  after-images 
are  coloured  with  the  shades  complementary  to  those  of  the 
objects. 

The  explanation  of  the  positive  after-image  of  a  white  object v 
probably  lies  in  the  fact,  which  we  have  already  noticed  in  another 
connection,  that  the  reaction  of  the  retina  does  not  cease  imme- 
diately the  stimulus  is  removed.  The  positive  image  is  merely  the 
after-discharge  of  the  light-sensitive  cells  in  the  retina.  The  pheno- 
menon of  the  negative  after-image  is  comparable  to  the  "rebound" 
which  occurs  after  a  reflex,  as  Sherrington  showed.  When  a  reflex 
arc  has  been  for  some  time  under  the  influence  of  one  reflex,  its 


COLOUR  VISION.  175 

responsiveness  to  a  stimulus  which  tends  to  bring  about  the  oppo- 
site reflex  becomes  increased.  Fatigue  following  a  reaction  of  one 
kind  makes  the  way  easier  for  the  opposing  reaction. 

In  more  detailed  form,  according  to  the  Young  theory,  the  reason  why  the 
after-image  of  a  coloured  object  is  tinged  with  the  complementary  colour  is  as 
follows.  During  the  time  that  the  gaze  was  fixed  on  the  object  all  three  com- 
ponents in  the  cells  of  the  retina  on  which  the  image  fell  were  being  stimulated  but 
the  component  or  components  which  are  most  sensitive  to  the  colour  of  the  object 
were  being  stimulated  most.  When  the  object  is  withdrawn  and  the  place  on 
which  the  image  falls  is  uniformly  stimulated  by  white  light  all  three  com- 
ponents respond.  The  one  which  was  mainly  affected  by  the  former  light  is 
fatigued  however  and  responds  less  than  the  others.  This  enables  the  colour 
complementary  to  it  to  come  into  prominence. 

PARTIAL  COLOUR  BLINDNESS. — This  abnormal  condition  of  vision  is  inter- 
esting in  the  discussion  of  the  theories  of  colour  vision  as  it  affords  a  comparison 
with  the  normal.  The  defect,  fairly  common  among  men,  less  so  in  women, 
is  physiologically  quite  different  from  total  colour  blindness,  with  which  it  must 
not  be  confused.  People  who  are  partially  colour  blind  distinguish  differences 
in  light  waves  of  different  lengths,  no  matter  whether  their  intensities  are  equal 
or  not,  but  they  see  fewer  differences  than  normal  people.  If  they  are  shown 
light  of  different  colours  (the  best  test  is  light  coming  from  lanterns  with  windows 
of  coloured  glass)  they  select  as  being  of  similar  shades  the  yellows  and  the  blues 
and  the  violets  which  look  much  alike  to  the  normal  eye,  but  in  choosing  shades 
similar  to  a  green  they  also  take,  as  well  as  other  green  lights,  different  shades  of 
red,  and  in  matching  a  red  standard  they  pick  out  as  having  a  colour  similar  to  it 
not  only  other  reds  but  also  green  as  well.  The  condition  of  their  light-  receptive 
mechanism  seems  to  be  not  so  much  different  from,  as  simpler  than,  the  normal; 
roughly  speaking,  partially  colour-blind  vision  is  a  reduction  form  of  ordinary 
sight.  Whereas  all  the  various  shades  which  one  sees  with  normal  colour  vision 
cannot  be  produced  with  combinations  of  less  than  three  given  colours,  two  only, 
if  mixed  in  different  proportions,  will  match  all  the  colours  seen  by  a  subject  who 
is  partially  colour-blind. 

There  are  two  types  of  the  defect.  In  the  first,  most  common,  form  the  eye 
is  relatively  insensitive  to  red  light.  To  match  an  olive  green,  people  with  this 
type  of  the  defect  choose  a  scarlet  which  to  the  ordinary  eye  appears  much  brighter 
and  the  visible  spectrum  is  shorter  for  them  at  the  red  end  than  it  is  for  other 
people.  Subjects  whose  vision  belongs  to  the  second  type  match  a  green  with  a 
red  which  is  about  equally  bright  and  the  red  end  of  the  spectrum  appears  to  have 
the  usual  length. 

The  explanation  of  these  facts,  according  to  the  theory  of  the  three  visual 
components,  is  that  in  eyes  of  the  first  type  the  red  component  is  left  out  and 
that  all  wave  lengths  have  only  the  other  two  components  to  act  upon.  In  the 
second  type  it  is  the  green  which  is  missing.  This  would  express  the  actual  con- 
ditions well  enough  if  only  these  abnormal  types  were  accurately,  and  not  merely 
approximately,  reduction  type  of  the  normal.  More  recent  work  however  has 


176  EXPERIMENTAL  PHYSIOLOGY. 

emphasized  the  fact  that  this  is  not  the  case  and  so  far  it  has  not  been  possible 
to  cover  adequately  the  conditions  of  the  defect  with  this,  or  indeed  with  any 
other,  theory. 

HERING'S  THEORY  OF  COLOUR  VISION. — The  only  other  theory  which  has 
rivalled  that  of  Young  as  a  starting  point  for  experimental  work  is  the  one  brought 
forward  by  Hering.  This  is  also  based  on  the  laws  of  colour  mixing  which  we  have 
already  outlined,  but  it  affords  as  well  some  physiological  explanation  for  the 
important  fact  that  in  our  sensations  light  may  not  only  be  divided  into  different 
colours,  but  these  again  appear  to  fall  into  two  great  classes,  the  'warm'  or 
'bright',  cheerful  colours  and  the  'cold'  or  'dull'  ones.  To  the  'warm'  class 
belong  reds,  oranges,  and  yellows;  they  are  bright  of  their  own  nature  as  it  were, 
quite  apart  from  the  brilliancy  with  which  they  are  lighted.  The  dull  ones  are 
green,  blue  and  violet.  There  are  many  examples  which  show  that  we  recognize 
this  inherent  brightness  or  dullness  of  colours  in  everyday  life.  We  "see  things 
through  rosy  spectacles"  or  we  "feel  blue".  Decorators  use  yellow  in  north 
rooms  with  no  sunlight,  but  blue  or  green  are  said  to  be  too  'cold';  children  are 
dressed  in  red  in  winter  because  it  is  "such  a  warm  colour".  The  suggestion 
which  Hering  made  was  this:  there  are  three  substances  in  the  retina  each  of 
which  may  be  changed  by  light  stimuli  in  two  ways,  being  either  built  up  or 
broken  down.  One  of  them  is  the  white-black  substance;  light  waves  of  more 
than  a  certain  intensity  break  this  down,  no  matter  what  their  length,  and  give 
as  a  result  the  sensation  of  white  light.  Darkness  causes  it  to  be  built  up  and  a 
sensation  of  blackness  arises  from  this.  Of  the  other  two  components,  one  is 
acted  on  only  by  red  light,  which  breaks  it  down  or  katabolises  it,  or  by  green,  the 
complementary  to  red,  which  builds  it  up.  Katabolism  of  the  third  substance 
is  caused  by  yellow  light,  anabolism  by  blue,  its  complementary.  All  other  colour 
sensations  are  mixtures  of  the  sensations  arising  from  the  anabolism  or  katabolism 
of  the  three  substances.  All  colours  which  break  down  the  components  are 
similar  to  white,  which  also  does  this;  that  is  why  they  are  specifically  bright. 
Colours  which  build  up  are  like  darkness  and  hence  in  themselves  are  dull.  Com- 
plementary colours  give  white  light  because,  since  they  act  equally  on  a  single 
substance,  the  katabolic  effect  of  one  cancels  the  anabolic  effect  of  the  other  and 
the  only  reaction  left  over  is  the  katabolism  which  they  both  bring  about  in  the 
white-black  substance. 

According  to  this  theory  the  reason  why  the  after-image  of,  for  instance,  a 
green  object  is  coloured  red  is  that  the  action  of  the  green  light  having  built  up  a 
great  deal  of  the  red-green  substance,  the  red  waves  contained  in  the  white  light 
from  the  bright  field  which  follows  have  more  substance  to  act  on  than  the  other 
waves.  The  after-image  of  a  yellow  object  is  blue  because  the  yellow  waves  have 
broken  down  the  yellow-blue  substance  to  a  great  extent  and  the  anabolic  reaction 
to  the  blue  waves  in  the  succeeding  light  is  more  intense,  tending  to  restore  the 
equilibrium,  than  it  would  be  if  the  equilibrium  had  been  undisturbed. 

This  theory  gains  some  support  from  other  observations  on  vision.  Blackness 
seems  to  us  to  be,  not  a  negative,  but  a  positive  thing.  In  the  ordinary  resting 
state  of  the  retina  we  do  not  see  blackness;  our  visual  field  is  covered  with  vague 


COLOUR  VISION.  177 

light-waves  and  is  roughly  speaking  grey,  certainly  not  pure  black,  as  it  ought  to 
be  as  far  as  the  Young  theory  goes.  According  to  the  Hering  theory  the  equili- 
brium of  the  white-black  substance  is  the  resting-state,  associated  with  grey  sen- 
sation, and  the  black  sensation  belongs  to  active  katabolism. 

When  it  comes  to  an  explanation  of  partial  colour-blindness  this  theory  breaks 
down.  Absence  of  the  red-green  component  would  be  the  most  obvious  explana- 
tion to  advance  but  this  does  not  hold  in  view  of  the  two  different  types  of  the 
defect.  There  are  also  difficulties  arising  from  more  detailed  experiments  on 
after-images  which  stand  in  the  way  of  accepting  this  theory  as  a  complete 
expression  of  the  facts  of  colour  vision.  Indeed  no  theory  has  as  yet  provided 
that,  a  fact  not  to  be  wondered  at  in  view  of  the  extreme  complexity  of  the  reac- 
tions involved 

Experiment  71. — Map  out  the  extent  of  the  colour  fields  on  the 
retina  by  using  the  perimeter.  This  consists  of  a  strip  of  metal 
bent  to  form  an  arc  which  can  be  rotated  in  various  meridians. 
The  arc  is  graduated  from  the  axis  and  it  carries  a  small  rider 
to  which  a  piece  of  white  or  tinted  paper  is  attached.  The 
observed  person  rests  his  chin  on  the  wooden  pillar  placed  in 
front  of  the  arc,  and  with  one  eye  closed  he  looks  steadily  at 
a  small  white  spot  marked  on  the  axis  of  the  instrument.  The 
observer,  moves  the  carrier  from  the  free  end  to  the  axis 
of  the  arc  slowly,  and  notes  the  exact  graduation  at  which  the 
subject  first  perceives  it.  This  distance  he  then  marks  on  a 
chart  which  consists  of  a  circle  with  various  diameters  repre- 
senting the  meridians  each  graduated  to  correspond  to  the  arc, 
from  the  centre  outwards. 

In  transferring  the  readings  to  the  chart,  allowance  must  be 
made  for  the  crossing  at  the  nodal  point  of  the  eye.  The  obser- 
vation is  repeated  for  at  least  twelve  different  meridians.  Having 
mapped  out  the  visual  field  for  white  (by  joining  the  marks  on 
the  chart)  the  observation  is  repeated  using  red,  yellow  and 
blue  papers  on  the  carrier. 


CHAPTER    XXII. 

SIMULTANEOUS  CONTRAST.    VISUAL  JUDGMENTS. 

In  the  foregoing  discussion  it  has  been  tacitly  assumed  that  the 
only  light  which  has  anything  to  do  with  the  visual  sensations 
which  arise  from  stimulation  of  any  particular  part  of  the  retina  is 
the  light  which  actually  falls  on  that  part.  As  a  matter  of  fact  this 
is  not  so.  Strong  stimulation  of  one  area,  as  well  as  causing  the 
appropriate  sensation  there,  also  tends  to  produce  sensations  of  the 
opposite  nature  in  the  parts  nearby. 
Experiment  72. — Take  two  pieces  of  the  same  paper,  neutral  grey 

in  colour,  and  lay  one  on  a  white,  and  one  on  a  black  back- 


FlG.  49.     To  show  simultaneous  contrast. 

ground.  The  first  appears  darker  and  the  second  lighter  than 
before  because  of  the  contrast  with  the  surrounding  field.  The 
effect  may  be  increased  by  veiling  the  whole  with  a  white  tissue 
paper. 

Experiment  73. — Arrange  a  white  background  with  a  horizontal 
row  of  candles  in  front  of  it  and  thrust  a  screen  in  from  one 
side,  part  way  between  the  two  (Fig.  49).  One  large  area 
of  the  background  (GH)  receives  none  of  the  candlelight  and  one 
(AB)  receives  light  from  all  the  candles.  Between  these  there 
are  a  number  of  vertical  strips,  on  the  first  of  "which  (FG)  the 
light  from  only  one  candle  falls,  on  the  second  the  light  from 
two  (EF),  and  so  on.  One  would  expect  each  of  these  strips  to 

178 


VISUAL  JUDGMENTS.  179 

seem  of  even  brightness  throughout;  actually  however,  as  the 
figure  shows,  each  one  appears  lighter  at  the  margin  which  is 
next  the  darker  area  and  darker  at  the  other  edge,  which 
borders  on  the  more  brightly  lighted  strip. 

Experiment  74. — Lay  the  piece  of  grey  paper  on  a  background  of 
bright  red.     Cover  them  both  with  white  tissue  paper.     The 
grey  area  looks  tinged  with  green-blue,  the  colour  complemen- 
tary  to   that  of   the   background.      Change   the   background 
several  times,  using  various  brilliant  colours,  and  note  what 
influence  each  has  on  the  apparent  colour  of  the  neutral  grey. 
The  phenomenon  of  simultaneous  contrast  is  seen  in  countless 
ways  in  ordinary  life.    Shadows  on  sand  in  the  sunlight  look  bright 
blue  because  of  their  yellow  back-ground.     So,  too,  places  in  a 
brightly  lighted  room  which  are  shaded  from  the  artificial  light 
but  faintly  illumined  by  daylight  appear  to  be  blue,  though  as  a 
matter  of  fact  the  light  falling  on  them  is  colourless,  only  because 
of  the  yellow  in  the  light  on  the  surrounding  areas  of  the  field. 
The  principal,   consciously  or  unconsciously,   is  used   in   art,   in 
posters  and  on  the  stage,  to  make  the  effect  of  vivid  colour  more 
vivid  or  to  modify  the  shade  of  fainter  ones.     It  is  not  clear  how 
the  phenomenon  is  brought  about.    It  does  not  happen  in  the  retina, 
for  simultaneous  contrast  has  been  shown  for  the  blind  spot, 
where  there  is  no  retina  at  all.    The  modification  must  take  place 
somewhere  on  that  part  of  the  brain  which  is  concerned  with  sight. 
In  this  connection  it  is  interesting  to  remember  that  there  are 
other  instances  of  the  activity  of  one  sensory  area  influencing  the 
sensitivity  of   another.     Sherrington   showed   the  stimulation  of 
one  part  of  a  receptive  field  lowered  the  threshold  of  the  response 
to  a  succeeding  stimulation  of  another  part  of  the  field,  for  the  same 
or  for  an  allied  reflex  (Immediate  Induction). 

Judgment  of  Space  and  Depth. — External  objects,  no  matter 
what  their  shape,  can  only  form  flat  images,  images  of  two  dimen- 
sions, on  the  retina.  In  spite  of  this  we  see  the  objects  in  three 
dimensions,  as  having  depth  as  well  as  width  and  height,  and  it  is 
of  interest  to  analyse  some  of  the  factors  which  contribute  to  this 
judgment  as  well  as  those  which  have  to  do  with  another  closely 
allied  to  it,  the  judgment  of  distance.  It  is  not  practicable  to  do 
in  the  class  room  many  of  the  experiments  on  the  factors  concerned 


180  EXPERIMENTAL  PHYSIOLOGY. 

in  visual   judgments   because   they   are   so   largely  subjective   in 

nature.    The  student  is  expected  to  make  observations  for  himself 

along  the  lines  indicated  below.     He  should  also  use  the  various 

charts  which  have  been  prepared  to  assist  in  this  part  of  the  work. 

Experiment  75. — Some  of  our  accuracy  depends  on  the  use  of 

both  eyes  together.      Try  to  touch  with  the  tip  of  your  pencil  a 

black  dot  in  the  middle  of  a  sheet  of  white  paper  which  you 

hold  obliquely  in  front  of  you.     Now  close  one  eye  and  see 

whether  or  not  you  can  perform  the  movement  as  well  as  before. 

MONOCULAR  ELEMENTS  IN  JUDGMENT  OF  DISTANCE.  —  One  of 

these  is  the  HAZINESS  or  clearness  of  the  air  between  the  object 

and  the  observer.    Objects  at  a  distance  are  hazier,  all  other  things 

being  equal,   than   those  near  by,   so  that  we  usually  interpret 

hazy  objects  as  being  distant.    That  is  why  objects  "loom  large" 

in  a  fog.     Since  the  things  look  hazy  we  conclude  that  they  are 

farther  away  than  they  really  are.     The  size  of  the  images  which 

they  cast  on  the  retina  is  not  changed,  however,  and  this  together 

with  our  idea  of  their  distance  is  the  only  clue  which  we  have  as 

to  the  size  of  the  objects.     If  they  were  really  as  far  away  as  we 

imagine  them  to  be,  to  throw  images  of  this  size  on  the  retina  they 

would  have  to  be  larger  than  they  really  are,  and  we  form  our 

judgments  accordingly. 

A  second  and  more  important  factor  in  monocular  judgment  is 
that  known  as  MATHEMATICAL  PERSPECTIVE.  It  is  familiar  that 
lines  which  are  really  parallel  to  one  another  appear  as  they  recede 
into  the  distance  to  come  closer  and  closer  together.  The  rails  of 
a  level  stretch  of  track,  for  instance,  appear  to  one  standing  be- 
tween them  to  form  a  V,  with  its  point  beyond  the  horizon.  We 
are  so  familiar  with  this  effect  of  distance  that  when  we  see  lines 
which  we  believe  to  be  parallel,  or  nearly  so,  appearing  much 
closer  together  at  the  farther  than  at  the  nearer  end  of  an  object, 
we  judge  the  object  to  have  a  good  deal  of  depth. 

THE  MUSCLE  SENSE  of  the  ciliary  muscles  gives  important 
information  as  to  the  depth  of  objects  which  are  close  at  hand, 
because  of  the  difference  in  the  extent  of  accommodation  necessary 
to  bring  into  focus  first  their  nearest  and  then  their  farthest  point. 
The  greater  depth  they  have,  the  more  difference  there  is  in  the 
effort  of  accommodation  in  the  two  cases. 


VISUAL  JUDGMENTS. 


181 


THE  SIZE  OF  FAMILIAR  OBJECTS  is  used  to  judge  distances.  If 
the  images  on  the  retina  of  people  or  animals  are  small  we  assume 
that  they  must  be  far  away  and  other  things  which  are  evidently 
near  them,  of  which  we  do  not  so  accurately  know  the  size,  are 
judged  also  to  be  distant. 

BINOCULAR  OR  STEREOSCOPIC  VISION. — When  we  look  with  both 
eyes  at  a  flat  object  the  image  which  is  thrown  on  one  retina  is  of 
exactly  the  same  shape  as  that  made  on  the  other.  If  the  object 
has  depth,  however,  the  two  images  are  not  exactly  alike.  The 
right  eye  sees  a  little  more  of  the  right  side  and  a  little  less  of  the 
left  than  the  left  eye  does,  and  vice  versa.  For  instance,  if  one 
looks  from  above  at  a  pyramid  with  its  top  cut  off,  the  right  eye 
receives  an  image  of  it  of  the  shape  of  diagram  A  in  Fig.  50,. 
the  left,  one  like  B.  Each  of  these  diagrams  alone  looks  perfectly 


FIG.  50.     To  illustrate  binocular  vision. 

flat.  But  hold  them  in  front  of  your  eyes  about  six  inches  away 
and  stare  straight  through  them,  relaxing  your  accommodation; 
the  two  appear  to  fuse  and  the  picture  that  results  is  one  of  a  pyra- 
mid which  has  depth  as  well  as  breadth  and  height.  This  is  in  all 
probability  the  main  factor  in  the  better  judgment  of  depth  which 
one  gets  from  using  both  eyes.  The  principle  is  used  in  the  stereo- 
scope. Two  photographs  are  taken  of  the  same  view,  but  the  first 
from  a  position  a  little  to  the  right  of  that  from  which  the  second 
is  taken,  the  distance  between  the  two  positions  being  greater  than 
the  distance  between  the  eyes.  These  pictures  are  mounted  on  a 
frame  and,  by  an  arrangement  of  prisms,  the  image  of  the  one  which 
was  taken  from  the  right  side  is  thrown  on  the  right  eye,  and  the 
image  of  the  left  picture  on  the  left.  The  result  is  a  view  in  which 
the  relief  or  depth  appears  even  greater  than  it  really  is. 


CHAPTER    XXIII. 
HEARING. 

Almost  all  that  is  known  about  the  physiology  of  hearing  has  been  got  by 
interpreting  the  structure  of  the  ear.  The  subject  lends  itself  hardly  at  all  to 
experimental  investigation  and  on  this  account  no  attempt  has  been  made  to  have 
this  chapter  similar  in  treatment  to  the  others.  It  is  inserted  merely  in  order  to 
round  out  for  the  student  the  outline  of  the  physiology  of  the  special  senses. 

THE  PHYSICAL  BASIS  OF  SOUND. 

Preliminary  to  the  consideration  of  the  ear  itself  the  student  is  reminded  of 
the  following  facts  in  the  physics  of  sound.  Sound,  like  light,  is  carried  by  waves, 
but  while  light  waves  are  strains  in  an  intangible  ether  and  have  nothing  to  do 
with  the  molecules  of  the  medium  in  which  they  travel,  sound  waves  are  vibra- 
tions of  the  medium  which  carries  them  and  they  do  not  pass  across  a  vacuum. 
The  vibrations  of  the  air  molecules  by  means  of  which  a  sound  wave  is  carried  are 
in  the  direction  in  which  the  wave  itself  is  travelling,  each  particle  swinging  to  and 
fro  alternately  in  front  of  and  behind  its  mean  position.  The  movement  of  the 
particles  close  to  the  source  of  the  sound  is  started  by  the  vibrations  of  the  source 
itself.  Those  molecules  in  turn  set  those  swinging  which  are  a  little  farther  away, 
these  communicate  the  movement  to  the  next,  and  so  the  wave  is  carried.  It 
follows  that  in  air  in  which  a  sound  wave  is  travelling  there  must  be  some  place 
where  the  number  of  air  molecules  is  greater  than  the  average  and  somewhere 
where  it  is  less,  alternate  places  of  compression  and  of  rarefaction  (Fig.  51.  No.  1). 
The  condition  in  the  column  of  air  at  any  one  time  may  be  shown  diagrammatically 
by  a  curve  such  as  in  Fig.  51,  No.  2.  Here,  lengths  along  the  abscissa  represent 
distances  from  the  source  along  the  line  of  the  wave;  lengths  along  the  ordinate 
show  the  number  of  molecules  per  unit  area.  Zero  represents  the  average  num- 
ber, lengths  above,  numbers  per  unit  area  greater  than  the  average  (compression), 
and  those  below,  numbers  less  than  the  average  (rarefaction).  If  the  sound 
is  musical  the  wave  will  be  a  regular  one  and  the  distance  from  one  crest  to 
another,  or  from  one  trough  to  another,  always  the  same.  Unmusical  sounds,  or 
noises,  are  made  by  waves  which  have  no  regular  shape. 

Between  musical  sounds,  which  will  chiefly  occupy  us,  it  will  be  seen  that 
there  are  several  possible  differences.  (1)  They  may  differ  in  rate,  that  is,  in  their 
distance  from  one  trough  of  the  wave  to  the  next,  or  from  one  crest  to  the  succeed- 
ing one.  The  rate  of  the  wave  determines  the  pitch  of  the  note;  the  faster  the 
wave  the  higher  the  note.  The  note  of  the  second  wave  in  Figure  52,  for  instance, 
whose  period  is  half  that  of  the  first,  is  an  octave  higher  than  the  first  one.  (2) 

182 


HEARING. 


183 


Waves  may  differ  in  intensity,  in  the  distance  from  zero  line  to  crest  or  trough; 
the  greater  the  intensity,  the  louder  the  note.  (3)  The  waves  may  be  musical, 
that  is,  each  single  wave  may  be  a  repetition  of  the  last,  and  still  not  have  the 
simple  form  shown  for  1  and  2  in  Fig.  52.  These  curves  are  such  as  would  be 
made  by  a  swinging  pendulum,  writing  on  an  evenly  moving  surface  and  they  are 
known  as  pendular  or  sine  curves.  The  sound  waves  which  a  tuning  fork  gives 
have  this  form.  Waves  3  and  4  in  Figure  52  on  the  other  hand,  are  musical  ones, 
but  not  of  this  simple  shape.  They  are  each  made  by  adding,  algebraically,  waves 
1  and  2  at  different  relative  phases.  Curve  3  is  got  by  adding  2  at  a'  to  1  at  A. 


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FIG.  51.  No.  1:  To  show  the  compression  and  rarefaction  in  the  air,  of  which  a 
sound  waveis  composed;  No.  2:  Diagram  to  express  the  conditions  in  No.  1  in  form 
of  a  curve. 

For  curve  4,  2  at  b'  was  added  to  1  at  A.  Obviously,  the  number  of  such  composite 
curves  which  one  might  make  is  unlimited,  since  one  can  also  choose  components 
of  different  relative  rates.  For  instance  the  period  of  one  might  be  to  the  period 
of  the  other,  as  one  to  three,  or  one  to  four,  or  two  to  five,  and  so  on.  Further, 
one  might  add  three  or  four  waves  together  instead  of  only  two.  The  period  of 
the  composite  is  always  that  of  the  slowest  component  wave  which  it  contains. 
The  low  note  is  known  as  the  fundamental.  It  is  the  shape  of  the  wave  which 


84 


EXPERIMENTAL  PHYSIOLOGY. 


FIG.  52.  Musical  sound  waves.  Nos.  1  and  2  are  simple  harmonic  curves;  Nos. 
3  and  4  are  composed  of  a  fundamental  of  the  period  of  No.  1  with  an  overtone  of 
the  period  of  No.  2  super-imposed  on  it  in  different  phases. 


FIG.  53.     Diagram  of  a  vibrating  violin-string  to  show  how  the  various  overtones  arise. 


HEARING.  185 

gives  it  its  quality.  If,  for  instance,  one  hears  middle  C  sounded  on  a  violin  it 
has  a  quality  different  to  that  of  the  same  note  on  the  piano,  and  this  again  is 
different  from  the  sound  of  the  tuning-fork,  which,  as  we  saw,  gave  a  simple 
pendular  curve.  The  reason  for  this  difference  is  that  none  of  the  sources  in 
the  common  instruments  swing  with  a  single  vibration.  A  violin  string,  for 
instance,  swings  as  a  whole,  the  rate  of  vibration  of  the  whole  length  determining 
the  pitch  of  the  lowest  or  fundamental  tone  in  the  composite  curve  of  its  note. 
As  well  as  this,  however,  the  string  tends  to  swing  as  if  it  were  subdivided  into 
short  lengths,  halves,  quarters,  thirds,  etc.  (Fig.  53).  The  points  dividing  these 
lengths  swing  with  the  vibration  of  the  whole;  the  parts  between  swing  with  the 
rhythm  of  the  whole  and  with  that  of  the  part  as  well.  The  rate  of  vibration  of 
the  divisions  is  to  the  rate  of  the  whole  inversely  as  the  length  of  the  division  is 
to  the  length  of  the  whole.  The  result  of  this  is  that  the  sound  wave  arising  from 
the  string  is  a  composite  one,  like  those  which  we  have  described,  made  up  of  a  sine 
curve  with  a  period  like  that  of  the  vibration  of  the  whole  string,  upon  which  a 
number  of  other  waves  have  been  superimposed,  waves  with  rates  in  simple 
arithmetical  ratios  (1/3,  1/4,  1/6,  etc.)  to  the  first.  These  arise  from  the  vibra- 
tions of  the  parts  and  are  known  as  the  OVERTONES.  It  is  the  number  and  in- 
tensity of  the.  overtones  which  determine  the  quality  of  the  note  and  it  is  because 
these  differ  on  different  instruments  that  we  are  able  to  distinguish  from  one 
another  the  notes  that  they  give. 

THE  TRANSMISSION  OF  SOUND  WAVES  IN  THE  EAR. 

Of  the  three  parts  of  the  ear,  the  external  and  middle  chambers  are  only 
concerned  with  the  transmission  of  the  sound  waves,  the  essential  organ  of  hearing 
being  entirely  contained  in  the  internal  ear.  The  waves  travel  in  air  as  far  as  the 
inner  end  of  the  EXTERNAL  AUDITORY  MEATUS.  Here  the  alternation  of  com- 
pression and  rarefication  of  which  they  are  made  up  sets  in  motion  the  TYMPANIC 
MEMBRANE.  This  membrane  is  made  up  of  two  epithelial  layers,  enclosing 
between  them  a  layer  of  connective  tissue  which  contains  both  radial  and  circular 
fibres.  In  shape  it  is  somewhat  peculiar,  being  slightly  vaulted,  with  its  convex 
side  inward.  The  apex  of  the  vault,  or  UMBO,  which  forms  a  centre  for  the 
radiating  and  circular  fibres,  is  not  exactly  at  the  middle  of  the  membrane  but  a 
little  above  it.  Because  of  its  peculiar  shape  the  membrane  responds  to  waves 
of  a  very  large  range  of  rates,  instead  of  having  a  strongly  marked  natural  period 
of  its  own  and  being  set  in  motion  mainly  by  waves  of  this  period,  as  would  be  the 
case  if  it  were  simply  a  flat  drum-head. 

THE  MIDDLE  EAR. — Sound  waves  travelling  in  the  middle  ear  are  no  longer 
carried  by  air  particles  but  by  the  swinging  of  a  chain  of  three  small  bones,  one 
end  of  which  is  fastened  to  the  end  of  the  tympanic  membrane  and  the  other  to 
the  membrane  of  the  fenestra  ovalis,  one  of  the  openings  in  the  bony  partition 
between  the  middle  and  the  inner  chambers.  The  connection  with  the  tympanic 
membrane  is  through  a  long  process,  the  manubrium  of  the  MALLEUS,  the  first  of 
the  three  bones.  The  body  of  a  malleus  is  connected  by  a  joint  with  the  second 


186 


EXPERIMENTAL  PHYSIOLOGY. 


H  *  a  d    of  m~ 


FIG.  54.     Diagram  of  the  bones  of  the  middle  ear. 


FIG.  55.     Diagram  of  a  lever  drawn  to  show  the  mode  of  action  of  the 
bones  of  the  middle  ear. 


HEARING.  187 

bone,  the  INCUS.  This  in  its  turn  is  in  connection,  by  a  process  running  down  and 
in,  with  the  third  bone,  the  STAPES,  the  inner  end  of  which  is  continuous  with  the 
membrane  of  the  fenestra  ovalis.  Fig.  54.  shows  the  shape  and  relationship  of 
the  three  bones.  The  malleus  is  rather  loosely  attached  by  a  ligament  to  the 
upper  part  of  the  outer  wall  of  the  chamber  and  besides  the  manubrium  it  has  a 
second  process,  a  slender  one,  nearly  at  right  angles  to  the  manubrium,  running 
forward  to  the  anterior  wall  and  firmly  bound  there.  The  bone  with  which  the 
body  of  the  malleus  is  joined,  the  incus,  has  two  processes,  one  of  which,  already 
mentioned,  extends  down  and  in  to  make  connection  with  the  stapes,  while  the 
other,  directed  backwards,  is  firmly  bound  to  the  posterior  wall  of  the  chamber. 
The  stapes  lies  almost  horizontally  between  the  tip  of  the  process  of  the  incus  and 
the  fenestra  ovalis.  The  whole  chain  of  bones  acts  together  as  a  lever,  one  arm  of 
which  is  the  manubrium  of  the  malleus,  the  other  the  downward  process  of  the 
incus,  together  with  the  stapes,  the  fulcrum  being  somewhere  in  the  lower  part  of 
the  malleus-incus  joint  (Fig.  55).  When  the  membrane  of  the  tympanum  swings 
in,  the  tip  of  the  manubrium  is  pressed  inwards.  This  would  tend  to  move 
malleus  and  incus  bodily  inwards  except  that  they  are  firmly  bound  in  an  antero- 
posterior  direction  by  the  attachment  of  the  processes  to  the  anterior  and  posterior 
walls  which  we  have  already  mentioned.  These  act  as  an  axis  around  which  the 
two  bones  swing.  When  the  tip  of  the  manubrium  is  moved  in,  the  head  of  the 
malleus  and  the  body  of  the  incus  swing  out.  Outward  movement  of  the  body 
of  the  incus  means  movement  in  of  the  process  which  is  attached  to  the  stapes, 
and  this  thrusts  the  stapes  ahead  of  it.  It  will  be  seen  in  the  diagram  that  the 
manubrium  (the  power  arm)  is  about  half  as  long  again  as  the  process  in  the  incus 
(the  load  arm).  The  lever  therefore  reduces  the  excursion  of  the  waves  which 
move  it,  but  at  the  same  time  it  increases  their  intensity.  Movements  com- 
municated to  the  fluids  of  the  internal  ear  need  only  be  very  tiny  indeed  to 
stimulate  the  sensitive  cells,  so  that  this  cutting  down  of  the  magnitude  of  the 
sound  waves  is  not  a  disadvantage.  At  the  same  time,  even  these  tiny  colums 
of  fluid  have  an  appreciable  inertia  and  on  this  account  the  increase  in  power  of 
the  wave  is  important.  A  further  increase  in  power  is  got  from  the  concentration 
of  the  force  of  the  wave  received  by  the  whole  surface  of  the  tympanic  membrane 
into  the  much  smaller  area  of  the  fenestra  ovalis. 

As  we  have  said,  a  movement  inwards  of  the  membrane  causes  the  head  of  the 
malleus  to  move  out,  locking  with  the  body  of  the  incus  and  drawing  it  along. 
If  the  membrane  is  moved  out  to  any  unusual  extent,  however,  as  happens  for 
instance  when  the  surrounding  pressure  falls,  the  inward  movement  of  the  head 
of  the  malleus  which  results  is  not  followed  by  the  incus.  As  Helmholtz  pointed 
out,  the  point  between  them  is  a  cog  or  ratchet  joint  and  locks  firmly  for  movements 
in  one  direction,  but  slides  for  large  movements  in  the  other.  This  is  probably 
important  as  a  protection  to  the  other  parts  of  the  middle,  and  to  the  internal,  ear. 

There  are  two  tiny  muscles  in  the  middle  ear.  One  of  these,  the  TENSOR 
TYMPANI,  has  its  origin  in  a  groove  above  the  Eustachian  tube,  that  is,  from  the 
inner  wall,  and  is  inserted  into  the  neck  of  the  malleus  below  the  axis  around  which 
the  bone  rotates.  When  this  contracts  it  must  draw  the  manubrium  of  the 


188  EXPERIMENTAL  PHYSIOLOGY. 

malleus  inward  and  through  it  exert  a  pull  on  the  membrane.  What  the  useful- 
ness is  of  this  extra  tension  on  the  membrane,  and  the  slight  increase  in  pressure 
of  the  middle  chamber  which  it  causes,  is  not  clearly  understood.  It  has  been 
suggested  that  the  action  is  protective,  damping  the  response  of  the  membrane 
to  excessive  sounds.  The  suggestion  has  also  been  made  that  the  muscle  con- 
tracts reflexly  when  the  attention  is  directed  to  sounds  of  high  pitch,  or  rapid 
vibrations,  to  increase  the  tension  of  the  membrane  and  thus  to  make  its  natural 
vibration  period  more  rapid.  The  second  muscle  in  the  middle  chamber,  the 
STAPEDIUS,  arises  from  a  projection  on  the  inner  wall  and  is  inserted  into  the  neck 
of  the  stapes,  on  which,  when  it  contracts,  it  exerts  a  lateral  pull.  The  conjectures 
as  to  the  use  of  the  tensor  tympani  apply  also  to  this  muscle. 

If  the  tympanic  membrane  is  to  swing  freely  in  response  to  sound  waves 
in  the  air  the  pressure  on  both  its  surfaces  must  be  kept  equal.  This  is  en- 
sured by  the  opening  of  the  EUSTACHIAN  TUBE  which  occurs  during  swallow- 
ing and  gives  a  communication  between  the  middle  ear  and  the  pharynx.  When 


^^ 

Frc.  56.     Cross  section  of  the  bony  labyrinth  showing  the  spiral  of  the  cochlea. 

the  mucous  membrane  of  the  tube  becomes  swollen  and  the  passage  closed, 
as  in  severe  colds,  the  gradual  absorption  which  goes  on  of  the  air  contained  in 
the  chamber  of  the  middle  ear  lowers  the  pressure  in  it,  the  membrane  no  longer 
vibrates  freely,  and  a  partial  deafness  results. 

PHYSIOLOGY  OF  THE  ESSENTIAL  ORGAN  OF  HEARING. 

THE  INTERNAL  EAR.  The  cavity  of  the  skull  which  contains  this  part  of  the 
labyrinth  is  spiral  in  shape,  gradually  tapering  off  to  a  point  (Fig.  56).  It  is 
lined  with  membrane  and  is  filled  with  fluid.  From  the  part  of  the  bone  which 
forms  the  central  pillar  of  the  spiral  a  ledge  projects  into  the  cavity,  reaching 
about  half  way  through  its  width  and  running  almost  the  entire  length  of  the  spiral. 
This  partial  partition  of  the  chamber  is  completed  by  two  membranes  attached 
at  one  side  to  the  ridge  of  bone  and  at  the  other  to  two  lines  a  little  distance  apart 
on  the  membrane  of  the  outer  wall  (Fig.  57).  As  a  result  the  fluid  of  the  spiral 


HEARING. 


189 


is  divided  into  three  columns,  one  on  one  side  of  the  partition  of  bony  ledge  and 
the  first  membrane,  one  on  the  other  side  of  the  bony  ledge  and  the  second  mem- 
brane, and  the  third,  enclosed  between  the  membranes,  roughly  triangular  in 
shape,  its  third  wall  being  made  by  the  membrane  of  the  outer  wall  itself.  Of 
the  two  outer  columns  one,  the  SCALA  VESTIBULI,  is  closed,  at  the  end  which  is 
directed  towards  the  middle  ear,  by  the  membrane  of  the  fenestra  ovalis  and  the 
other,  the  SCALA  TYMPANI,  by  the  second  membrane-covered  opening  in  the  parti- 
tion, the  fenestra  rotunda.  At  the  top  of  the  spiral  these  two  columns  commun- 
icate over  the  tip  of  the  middle  triangular  one,  which  ends  blindly  a  little  short  of 
the  upper  end.  Fig.  58  shows  diagrammatically  the  relationship  of  the  three. 
Movements  of  the  membrane  of  the  fenestra  ovalis  cause  vibrations  of  the  same 


FIG.  57.     One  turn  of  the  cochlear  spiral,  enlarged  to  show  the  organ  of  Corti. 


rate  and  shape  in  the  double  column  of  fluid  contained  in  the  two  outer  chambers, 
play  being  allowed  by  the  membranous  end  of  the  second  column  at  the  fenestra 
rotunda,  which  moves  out  when  the  ovalis  moves  in  and  vice  versa.  Because  the 
partitions  between  them  are  only  membranes,  it  is  to  be  expected  that  the 
oscillations  of  the  two  enclosing  columns  must  affect  the  contents  of  the  third. 
It  is  among  these  structures  that  the  endings  of  the  auditory  nerve  are  found  and 
we  must  look  here  for  the  essential  organ  of  hearing. 


190  EXPERIMENTAL  PHYSIOLOGY. 

Of  the  two  membranes  which  form  the  walls  of  this  triangular  chamber 
(Fig.  57)  one  is  histologically  quite  simple.  The  other,  the  BASILAR  MEMBRANE 
supports  a  double  row  of  pillars,  standing  with  their  bases  apart  and  their  tips 
leaning  together  and  projecting  into  the  fluid  of  the  middle  column,  the  endolymph. 
These  are  known  as  the  PILLARS  OF  CORTI.  Above  these  pillars  on  either  side, 
supported  by  the  tent-like  roof  which  they  form,  are  several  rows  of  cells,  among 
them  a  large  number  which  have  hair-like  projections  up  into  the  endolymph, 
The  whole  is  known  as  the  ORGAN  OF  CORTI.  The  fibres  of  the  auditory  nerve, 
which  runs  within  the  inner  pillar  of  the  spiral,  pass  out  by  the  bony  projection 
along  its  entire  length  and  end  in  the  hair  cells,  which  must  therefore  be  the  cells 
sensitive  to  the  waves  of  sound. 

As  we  have  already  seen,  the  ear  is  capable  of  distinguishing  not  only  pitch 
and  intensity  but  also  quality,  in  any  waves  which  it  receives.  Not  only  do 
notes  of  the  same  pitch,  one  without  and  one  with  many  overtones,  not  sound 
alike  but  with  training  the  hearer  can  distinguish  what  the  various  overtones  in 
the  notes  are,  so  that  our  theory  of  hearing  must  afford  a  physiological  basis  for 
this  analysis.  We  have  no  problem  of  simplification  to  deal  with  in  the  ear  as  we 
had  in  the  eye;  in  hearing  the  sensations  are  as  numerous  as  the  stimuli  which 
evoke  them.  The  most  generally  accepted  theory  is  one  proposed  by  Helmholtz, 
the  resonance  theory.  If  one  places  a  number  of  tuning  forks  of  different  periods 
near  a  vibrating  fork  or  reed,  giving  out  a  simple  note,  among  those  forks  which 
have  not  been  struck  the  one  with  the  same  natural  period  will  begin  to  vibrate 
and  give  out  its  note,  while  the  others  remain  silent.  If  the  vibrating  source  is  a 

f.  0  u-a,  1 1  a 


FIG.    58.     Diagram  of  the  relationship  of  the  three  fluid  columns  of  the  internal  ear. 

violin-string,  which  gives  a  note  with  overtones,  not  only  will  the  fork  with  a 
period  like  the  fundamental  respond  but  those  with  periods  equal  to  each  over- 
tone as  well.  Helmholtz  suggested  that  some  such  apparatus  must  be  contained 
in  the  ear.  He  at  first  thought  that  it  was  the  rods  of  Corti  which,  having  each 
a  different  natural  period,  acted  as  resonators  to  the  composite  vibrations  of  the 
fluid  of  the  outer  columns.  The  ear  however  is  capable  of  distinguishing  more 
notes  than  there  are  rods;  besides,  rods  are  absent  from  the  ears  of  singing  birds, 
and  this  idea  had  to  be  abandoned.  It  was  then  suggested  that  the  resonators 
might  be  found  in  the  basilar  membrane  itself.  It  contains  a  series  of  radial 
fibres  running  from  the  bony  ledge  to  the  outer  wall  and  the  width  of  the  mem- 
brane, and  therefore  the  length  of  these  fibres,  increases  progressively  from  the 
base  of  the  spiral  to  its  apex.  If  these  fibres  are  the  resonators  the  arrangement 


HEARING.  191 

is  like  that  of  the  strings  in  a  tiny  piano,  with  the  short  treble  ones  at  the  bottom 
of  the  cochlea  and  the  bass  ones  at  its  top.  The  difficulty  is  to  see  how  even  the 
longest  of  these  very  small  fibres  can  have  a  natural  period  as  slow  as  that  of  the 
lowest  note  which  we  can  hear.  Of  course  the  period  of  them  all  is  increased 
because  of  the  fluid  about  them  but,  even  so,  the  difficulty  has  not  been  com- 
pletely met. 

FUNCTION  OF  THE  SEMICIRCULAR  CANALS. 

Experiment  76. — Place  a  frog  on  a  glass  plate  and  cover  with  a 
funnel  or  beaker.  Rotate  about  longitudinal,  transverse  and 
vertical  axes  (referred  to  frog's  body),  and  notice  compensatory 
movements. 

Expose  one  of  the  white  otolithic  masses  in  an  anesthetized 
frog  by  removing  the  cartilage  after  slitting  the  mucous  mem- 
brane of  the  roof  of  the  mouth  medially  from  the  Eustachian 
tube.  Remove  one  otolithic  mass  in  one  'frog  and  both  masses 
in  a  second  frog.  After  recovery  from  the  anesthesic  compare 
the  compensatory  movements  and  equilibration  with  a  normal 
frog  when  rotated  in  the  different  axes,  and  when  swimming. 

COMPENSATORY  MOVEMENTS  IN  MAN. 

Experiment  77. — Let  the  subject  sit  in  a  swivel  chair  in  which 
he  is  rotated  10  to  20  seconds.  Describe  his  movements  after 
the  chair  stops.  Let  the  subject  describe  his  sensations  during 
and  after  the  rotation  with  and  without  the  eyes  closed. 


CHAPTER   XXIV. 

SKIN  SENSATIONS.     TASTE 

There  are  three  types  of  skin  sensations,  the  appreciation  of 
differences  of  temperature  (temperature  sense),  the  sense  of  touch, 
and  the  sense  of  pain.  Since  our  knowledge  of  the  normal  behaviour 
of  each  of  these  senses  depends  on  subjective  phenomena,  each 
student  must  perform  the  fundamental  experiments  as  given  below, 
both  on  himself  and  on  others,  and  must  accurately  describe  the 
results  in  his  notes. 

TEMPERATURE  SENSE. 

It  is  the  rate  at  which  heat  is  being  gained  or  lost  by  the  skin, 
and  not  the  actual  degree  of  temperature  of  the  applied  object, 
that  is  determined  by  our  sensations. 

Experiment  78.— Place  a  finger  of  one  hand  in  water  at  2°  C. 
and  the  corresponding  finger  of  the  other  hand  in  water  at  40°  C. 
After  no  temperature  sensations  are  felt  by  either  finger,  transfer 
them  simultaneously  at  30°  C.  Note  the  nature  of  resulting 
temperature  sensations  in  the  two  fingers. 

The  temperature  sensations  are  received  by  "hot"  and  "cold" 
spots  scattered  over  the  skin,  the  cold  spots  being  the  more  numer- 
ous (Fig.  59). 

Experiment  79. — Mark  out  an  area  of  skin  on  the  back  of  the 
hand,  say  20  X20  mm.  square.  The  hand  should  be  resting  com- 
fortably on  a  table  and  the  subject  blindfolded.  With  a  thermo- 
aesthesiometer  (a  test  tube  drawn  out  to  a  point  will  serve  the 
purpose),  containing  water  at  40°  C.,  proceed  to  explore  the 
selected  area,  systematically,  in  parallel  lines,  marking  with  ink 
the  spots  at  which  a  distinct  sensation  of  warmth  is  experienced. 
When  all  the  area  has  been  explored  accurately,  transfer  the 
spots  to  ruled  paper,  and  with  the  aesthesiometer  containing 
water  at  a  temperature  of  15°  C.,  proceed  in  the  same  way  to 
determine  the  cold  spots.  Note  that  the  cold  spots,  besides 

192 


SKIN  SENSATIONS. 


193 


being  more  numerous,  are  more  sharply  defined  than  those  of 
warmth;  the  latter  are  also  much  more  readily  fatigued.     This 
fact  must  be  remembered  in  repeating  the  observations. 
More  intense  heat  stimuli,  besides  stimulating  the  warm  spots, 

also  stimulate  those  of  jgold   causing  a  cold  sensatio 

Experiment  80. 


Test  this  using  a  temperature  of  about  50°  C, 
Mechanical  and  electrical  stimuli,  etc.,  applied  to  hot  and  cold 
spots,  may  call  forth  thermic  sensations. 

Experiment  81.  —  Select  a  few  pronounced  cold  and  hot  spots. 
and  stimulate  them  by  tapping  lightly  with  a  small  round 
pointed  object,  or  by  applying  the  tetanizing  electric  current. 


IP 


FIG.  59.  Heat  and  cold  spots  on  the  skin  of  the  palm  of  the  left  hand:  (a) 
heatspots;  (b)  cold  spots.  The  depth  of  the  shading  in  each  case  represents  the 
intensity  of  the  sensation. 

The  sensation  of  temperature  remains  for  some  time  after  the 
condition  causing  it  has   been  removed  (temperature  after-sensa- 
tions). 
Experiment  82. — Place  on  the  forehead  a  coin  which  has  been 

either  cooled  or  warmed,  and  note  the  nature  of  the  sensations 

which  are  experienced  after  its  removal. 

The  temperature  sense  is  not  equally  acute  over  the  body. 
Many  factors  influence  the  acuity  but  in  general  it  may  be  stated 
that  clothed  parts  are  more  sensitive  than  unclothed,  with  the 


194  EXPERIMENTAL  PHYSIOLOGY. 

exception  of  the  temples,  the  lower  eyelids  and  the  cheeks.     The 
midline  of  the  body  is  relatively  insensitive.     The  sensivity  in- 
creases from  the  far  extremity  of  the  limbs  towards  the  trunk. 
Experiment  83. — Using    test    tubes    containing    warm    or    cold 
water,  proceed  to  confirm  the  above  statements. 

SENSE  OF  TOUCH. 

This  is  likewise  mediated  by  spots  (touch  spots),  which  are  dis- 
tributed independently  of  those  of  temperature,  and  are  most 
numerous  to  the  "windward"  side  of  the  hair  follicles. 


FIG.  60.     Hair  aesthesiometers. 

Experiment  84. — Using  the  same  area  of  hand  as  was  employed 
for  determining  the  temperature  spots,  or  a  part  of  it,  make 
an  exact  chart  indicating  the  position  of  the  hairs  (use  a  lens  for 
this  purpose).  Now  cut  the  hairs  flush  with  the  skin,  by  means 
of  a  sharp  scissors,  or  shave  the  part.  Take  a  series  of  hair 
aesthesiometers  made  by  mounting  straight  hairs  of  varying 
thickness  at  right  angles  on  wooden  holders  (Fig.  60).  The 
exact  weight  at  which  each  hair  bends  when  pressed  on  one  scale 
pan  of  a  balance  is  marked  on  the  handle.  Select  a  hair  which 
provides  a  stimulus  of  such  a  strength  that  it  will  call  forth  the 


SKIN  SENSATIONS.  195 

peculiar  sensation  due  to  a  touch  spot.  Having  made  certain 
that  the  subject  who  should  be  blindfolded,  can  recognize  this 
sensation  (and  does  not  confuse  it  with  one  of  pain,  which  is  of 
longer  duration),  proceed,  systematically,  to  mark  the  touch 
spots.  Transfer  the  results  to  the  chart,  and  note  the  relation- 
ship of  the  touch  spots  to  the  hair  follicles.  By  touching  a  hair 
the  sense  of  touch  is  accentuated.  Repeat  these  observations 
on  the  calf  of  the  leg,  where  the  hair  follicles  are  less  numerous. 
Experiment  85. — Select  an  aesthesiometer  which  can  produce 
a  distinct  sensation  of  touch  when  its  hair  is  pressed  to  the 
bending  point  on  the  end  of  one  of  the  skin  hairs.  Apply  it  to  a 
hairless  part  of  the  skin  and  note  that  it  elicits  no  sensation. 
It  is  important  to  distinguish  between  the  sensations  of  deep 
pressure  and  touch. 

Experiment  86. — -Touch  the  skin  lightly  with  a  blunt  point;  then 
gradually  increase  the  pressure  and  note  the  occurrence  of  the 
deep  pressure  sensation.     Note  that  this  occurs  only  after  there 
has  been  decided  deformation  of  the  surface. 
The  threshold  value  for  touch  (touch  acuity)  varies  in  different 
parts  of  the  body.     Several  things,  besides  the  presence  of  hairs, 
determine  this  (thickness  of  skin,  rate  of  application  of  stimulus, 
previous  friction  of  skin,  etc.).     In  general,  however,  the  order  of 
touch  thresholds  is  as  follows:  lips,  finger  tips  and  forehead;  dorsal 
aspect  of  finger;  palm,  arm  and  thigh;  forearm;  while  much  less 
sensitive  are  the  extensor  surfaces  of  the  forearm  and  the  loins. 
Experiment  87. — Using  various  hairs,  determine  the  exact  thres- 
hold value  for  touch  for  the  above  regions  by  finding  what  thickness 
of  hair  must  be  used  to  elicit  the  sensation  of  touch  at  the  point 
at  which  the  hair  just  bends.     Make  a  table  of  the  results* 
giving  the  "bending  weight"  of  the  hairs  for  each  region. 
Besides  touch  acuity  it  is  important  to  study  the  LOCALIZATION 
of  touch  sensations.     This   may  be  done  either  by  asking  the 
(blindfolded)  person  to  point  with  his  finger  to  the  exact  place 
where  he  was  touched  (absolute  localization)  or  by  ascertaining 
the  distance  by  which  two  points  must  be  separated  in  order  to 


*In  many  of  these  experiments  on  touch  a  fine  camel's  hair  brush  can  also 
be  used. 


196  EXPERIMENTAL  PHYSIOLOGY. 

bed  iscriminated  (touch  discrimination).     This  "local  sign",  as  it 

is  called,  varies  in  different  parts  of  the  body. 

Experiment  88. — With  a  pair  of  calipers,  determine  this  distance 
for  the  tip  of  the  tongue,  the  palmar  surface  of  the  third  phalanx 
of  the  finger,  its  dorsal  surface,  the  tip  of  the  nose,  the  back  and 
upper  arm;  make  a  table  of  the  results.  Note  that  the  order 
of  sensitivity  for  touch  discrimination  is  not  the  same  as  that 
for  touch  acuity. 

SENSE  OF  PAIN. 

Any  stimulus  will  cause  pain  when  it  is  very  intense.  This  does 
not  mean,  as  has  been  thought,  that  pain  is  merely  due  to  over- 
stimulation  of  any  receptors.  There  are  special  receptors  for  pain, 
just  as  there  are  for  touch  and  temperature.  One  of  the  main 
proofs  of  this  is  that  pain  spots  are  more  extensively  and  regularly 
distributed  than  the  others. 

Experiment  89. — Using  the  same  area  of  skin  as  was  employed 
for  the  location  of  temperature  and  touch  spots,  proceed  to  mark 
out  the  pain  spots  by  pricking  with  a  stout  horse  hair  or  a  bristle. 
Note  that  the  sensation  is  more  lasting  than  that  for  touch  and 
that  the  pain  spots  are  distributed  in  a  different  manner. 
Another  proof  of  the  separate  existence  of  pain  spots  is  that  they 
alone  are  found  in  the  cornea;  on  the  conjunctiva  they  exist  along 
with  temperature  spots. 

Experiment  90. — Verify  the  above  statement,  using  medium 
hairs. 

The  skin  sensations  are  not  at  all  influenced  to  the  same  ex- 
tent when  the  blood  supply  is  interfered  with.     This  fact  becomes 
of   interest   on   account   of   its  analogy  to  the  results  which  have 
been  observed  during  the  regeneration  of  severed  nerves. 
Experiment  91. — By  means  of  a  blood   pressure  cuff  and   bulb 
applied  to  the  arm,  determine  the  systolic  pressure,  then  release 
the  pressure  and  raise  the  arm  so  as  to  empty  it  of  some  of  its 
blood,  after  which  again  apply  the  pressure  (but  not  above  the 
systolic  value).     Proceed  to  compare  the  sensations  of  touch, 
temperature  and  pain  in  exactly  corresponding  skin  areas  of  the 
two  hands.     Differences  may  take  some  time  to  become  evident. 
Note  particularly  for  which  sensations  they  first  become  so. 


SKIN  SENSATIONS  197 

TASTE. 

Closely  allied  to  the  skin  sensations  are  those  of  taste  and  smell. 
The  following  experiments  on  taste  are  important. 
Experiment  92. — (a)  Dry  the  tongue  and  apply  a  crystal  of  salt 

or  sugar.     Note  that  it  is  not  tasted. 

(b)  On  the  dry  surface  of  the  tongue  apply  by  means  of  a 
camel's  hair  brush  a  solution  of  quinine  (1  to  1,000),  sodium 
chloride  (1  to  200),  cane  sugar  (1  to  50),  and  sulphuric  acid 
(1  to  1,000).     Determine  at  which  part  of  the  tongue  the  strong- 
est sensation  is  produced  by  each. 

(c)  Prepare   a  series  of   solutions  of   gradually   increasing 
strengths  of  quinine,  salt,  sugar,  and  sulphuric  acid,  beginning 
in  each  case  at  1  in  5,000,  and  apply  to  that  portion  of  the  tongue 
most  sensitive  to  the  respective  substances.     Determine  what 
strength  of  solution  is  necessary  to  stimulate  taste. 

(d)  Apply  with  a  brush  a  little  of  the  sugar  solution  of  the 
strength  which  just  stimulated  taste,  and  follow  with  a  drop  of 
salt  solution  of  the  same  taste  value.     Note  that  the  salt  neu- 
tralizes the  effect  of  the  sugar  and  neither  is  tasted. 

(e)  Take  a  solution  of  strong  salt  water  into  the  mouth  and 
wash  out  with  distilled  water.      Note   that   the  water  tastes 
sweet  (negative  after-stimulation). 

PRESSURE. 

Experiment  93.— Weber's  Law.— With  the  hand  outstretched  on 
the  table  and  palm  upward,  the  subject  being  blindfolded,  a 
piece  of  cardboard  4  cm.  square  is  placed  on  the  finger  tips. 

With  5  gms.  as  the  standard  determine  the  least  increment 
necessary  to  detect  a  difference.  In  all  of  these  observations 
no  muscualr  effort  must  be  made;  moreover  the  weights  must 
be  applied  as  gently  as  possible. 

Determine    the    increments    necessary    for    the    following 
standards:  10  gm.,  50  gm.,  100  gm.,  200  gm.,  1,000  gm. 
Pressure  and  Muscular  Sense. — Repeat  the  above  observa- 
tions with  the  hand  removed  from  the  table,  the  muscles  of  the 
hand   and   arm   being   used   to   their   utmost   in   determining   the 
threshold  of  difference. 


SECTION   VI. 

DEMONSTRATIONS. 

In  the  foregoing  chapters  experiments  have  been  described 
which  the  student,  either  individually  or  in  small  groups,  can 
perform  for  himself,  but  there  are  other  experiments  of  equal  im- 
portance from  an  educational  viewpoint,  in  which,  for  obvious 
reasons  this  is  impossible  and  it  is  necessary  that  these  be  demon- 
strated. The  value  of  demonstrations  of  more  or  less  complicated 
experiments  in  physiology  depends  on  two  factors,  first,  that  the 
student  is  familiar  with  the  general  technique  of  the  methods  em- 
ployed, and  secondly  that  the  precise  application  and  bearing  of 
the  results  of  each  experiment  are  appreciated  by  him.  To  stage 
an  experiment  with  the  sole  object  of  demonstrating  results  is 
valueless,  however  important  and  fundamental  these  results  in 
themselves  may  be ;  the  demonstration  becomes  of  value  only  when 
the  student  knows  exactly  how  the  result  is  obtained  and  is  able 
to  place  it  in  relationship  with  previous  knowledge  gained  by  other 
methods  of  study. 

The  particular  experiments  which  it  may  be  deemed  advanta- 
geous to  demonstrate  will  necessarily  vary,  not  only  in  different 
laboratories,  but  also  from  year  to  year  in  the  same  laboratory.  It  is 
believed,  however,  that  it  will  be  useful  to  describe  briefly  the 
fundamental  experiments  that  the  authors  are  accustomed  to 
demonstrate  to  their  classes,  partly  to  assist  the  students  to  under- 
stand what  is  being  done,  and  partly  as  a  guide  to  others.  The 
experiments  that  have  been  selected  may  also  be  performed  by 
advanced  students  and  are  described  in  sufficient  detail  for  this 
purpose. 

The  demonstrations  are  grouped  in  chapters,  each  chapter 
giving  in  practicable  sequence  the  experiments  which  can  most 
conveniently  be  performed  on  a  single  animal. 


198 


CHAPTER    XXV. 

THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH,  AND 
THE  RESPIRATION. 

The  Reflex  Nerve  Control  of  the  Circulation  and  of  the 
Respiratory  Movements. 

In  Exp.  35,  p.  79,  it  has  been  demonstrated  that  the  heart 
beat  is  controlled  largely  through  the  vagus  nerve  and  that  the 
degree  of  resistance  to  the  blood  flow  through  the  splanchnic 
vessels  depends  on  impulses  carried  by  the  splanchnic  nerves. 
The  vagus  and  vaso-motor  nerves  arise  in  the  medulla  oblongata. 
The  efferent  nerves  of  the  respiratory  muscles  (phrenic  and  inter- 
costal nerves)  arise  in  spinal  nerve  centres,  which  are  dominated 
by  a  higher  centre.  This  chief  respiratory  centre,  as  it  is  called, 
is  also  situated  in  the  medulla.  The  present  experiment  is  devised 
to  throw  light  on  the  afferent  pathways  through  which  the  above 
centres  become  stimulated. 

Demonstration  1. — Simultaneous  tracings  are  taken  of  the 
carotid  blood  pressure  and  of  the  respiratory  movements  (p.  97), 
in  an  etherised  and  tracheotomised  dog.  The  sciatic  nerve  in 
one  leg  and  the  vagus  nerves  on  both  sides  of  the  neck  are  exposed 
and  loose  ligatures  placed  around  them.  A  hot  iron  is  then  applied 
to  the  skin  of  the  foot  while  the  recording  drum  is  revolving  at 
such  a  speed  that  the  cardiac  pulsations  can  readily  be  counted. 
Observe  the  effects  on:  (1)  the  pulse  rate  (2)  the  mean  arterial 
blood  pressure  and  (3)  the  rate  and  depth  of  the  respirations. 
What  general  conclusions  may  be  drawn  concerning  the  influence 
on  the  centres  of  over-stimulation  of  skin  nerves? 

After  moderately  tightening  the  ligature,  the  sciatic  nerve  is 
cut  peripheral  to  it  and  the  hot  iron  reapplied  to  the  skin.  What 
conclusion  do  you  draw  from  the  results? 

The  central  end  of  the  cut  sciatic  is  then  stimulated  with  the 
faradic  current,  of  a  strength  which  just  produces  some  change  in 

199 


200  EXPERIMENTAL  PHYSIOLOGY 

one  or  other  of  the  tracings,  the  observations  being  repeated  with 
stronger  stimuli.  The  respirations  are  invariably  increased  in 
depth  and  rhythm  (hyperpnoea)  and  the  heart  rate  is  often  reduced 
but  the  effect  on  blood  pressure  as  a  rule  is  not  readily  measurable, 
because  of  the  exaggerated  respiratory  oscillations  which  the 
tracing  shows.  Afferent  fibres  to  the  vagus  and  respiratory  centres 
are  demonstrated  in  this  experiment,  and  those  to  the  vasomotor 
centre  can  be  inferred  in  cases  where  the  blood  pressure  rises  or 
remains  constant,  while  the  pulse  becomes  slower.  Why  is  the 
conclusion  permissible? 

One  vagus  nerve  is  cut  after  moderately  tightening  the  ligature 
around  it  and  the  central  end  is  stimulated.  Are  the  results  similar 
to  those  of  sciatic  stimulation? 

The  results  of  the  foregoing  experiments  indicate  that  the 
centres  of  respiration  and  of  vagus  and  vasomotor  control  are 
simultaneously  stimulated  through  afferent  nerves.  In  order  to 
determine  the  relative  importance  of  each  effect  it  is  necessary 
to  eliminate  one  or  both  of  the  other  afferent  influences.  With 
this  object  in  view,  the  remaining  vagus  is  cut  so  as  to  remove  the 
heart  from  vagus  control.  (What  drugs  could  have  been  employed 
to  effect  a  similar  denervation  of  the  heart?  Why  is  there  a  rise 
in  blood  pressure?)  The  sciatic  and  vagus  nerves  are  again  stimu- 
lated. What  difference  is  there  in  the  results?  Explain  the  cause. 

Frequently,  by  using  induced  shocks  that  are  relatively  slow 
and  feeble,  the  reflex  effects  on  arterial  blood  pressure  are  the 
opposite  of  those  observed  when  shocks  of  ordinary  frequency  and 
strength  are  employed.  What  conclusions  do  you  draw? 

Even  the  elimination  of  reflex  vagus  effects  may  not  suffice  to 
demonstrate  the  pressor  or  depressor  influence  because  of  the  pre- 
dominance of  the  respiratory  effects.  It  may  be  necessary  to 
eliminate  the  latter,  which  can  be  done  by  injecting  through  the 
femoral  vein  a  saturated  solution  of  curare  in  physiological  saline.* 
Under  the  influence  of  curare  the  respirations  cease,  and  to  keep  the 
animal  alive  it  is  necessary  to  connect  the  respiratory  pump  to  the 
tracheal  cannula,  with  the  anaesthetic  bottle  inserted  in  the  tubing. 

*The  curare  solution  should  be  prepared  several  days  previously  and  should  be 
tested  on  a  frog  before  using  in  the  above  experiment.  The  curare  at  present  on 
the  market  is  very  unreliable. 


VASCULAR  AND  RESPIRATORY  ORGANS.  201 

(Etherisation  must  be  maintained,  otherwise  the  animal  might 
suffer  pain.  Why?) 

While  maintaining  the  artificial  respiration  the  sciatic  and 
vagus  nerves  are  stimulated  as  before.  What  conclusions  can  be 
drawn  from  the  results? 

The  effect  of  asphyxia  on  the  arterial  blood  pressure  is  then 
studied,  the  asphyxia  being  induced  by  suspending  the  artificial 
respiration.  How  do  the  results  compare  with  those  observed 
during  asphyxia  with  the  vagi  intact?  After  the  blood  pressure 
has  finally  fallen  to  zero  the  thorax  is  opened  and  the  heart  ex- 
amined. Extreme  venous  engorgement  is  observed.  Note  the 
behaviour  of  the  heart  when  the  engorgement  is  relieved  by  punc- 
turing the  right  ventricle.  What  conclusions  do  the  observations 
warrant? 


CHAPTER   XXVI. 

The   Direct   Demonstration   of   Vasoconstrictor  Fibres   by 
the  Plethysmographic  Method. 

Demonstration  2. — The  abdomen  is  opened  in  an  etherised, 
tracheotomised  dog  and  the  intestines  retracted  to  the  left  side 
under  towels  wrung  out  in  warm  saline  solution.  The  great  splanch- 
nic nerve  is  isolated  and  a  ligature  placed  around  it  on  the  right 
side  (see  p.  83).  The  right  kidney  is  freed  from  its  bed  and  the  folds 
of  peritoneum  running  to  its  upper  end  are  cut  after  applying  mass 
ligatures.  The  pedicle  is  carefully  freed  by  blunt  dissection  and 
the  plexus  of  nerves  isolated  from  it  and  a  ligature  placed  around 
them.  An  oncometer,  with  cotton  wool  well  mixed  with  vaseline 
laid  in  the  groove  for  the  pedicle,  is  then  placed  under  the  viscus 
and  more  cotton  and  vaseline  placed  in  the  groove  until  this  is 
filled  (without  any  compression  of  the  vein  or  ureter)  after  which  the 
glass  lid  is  applied  and  clamped  down.  (There  must  be  no  strain  or 
kinking  of  the  vessels  during  the  manipulation).  The  side  tube  of 
the  apparatus  is  finally  connected  by  moderately  thick  walled 
tubing  with  a  bellows  recorder,  the  writing  style  of  which  is  accur- 
ately adjusted  in  the  same  perpendicular  with  the  writing  style  of 
a  mercury  manometer  connected  with  the  carotid  artery.  A  re- 
spiratory tracing  should  also  be  taken.  On  a  moderately  fast  drum 
tracings  are  taken  to  show  the  relationship  of  the  oscillations  of 
the  oncograph  to  the  arterial  and  respiratory  tracings.  (What  is 
the  relationship?) 

The  effect  produced  on  the  kidney  volume  and  the  arterial 
blood  pressure  is  then  observed:  (1)  during  (electrical)  stimulation 
of  the  vagus  in  the  neck;  (2)  during  stimulation  of  the  great  splanch- 
nic nerve  on  the  right  side  (Fig.  61),  and  (3)  during  stimulation  of 
the  renal  nerves.  How  do  you  interpret  the  results?  Why  is  the 
arterial  blood  pressure  essential  in  the  interpretation? 

A  small  amount  of  physiological  saline  containing  1-10,000 
adrenalin  chloride  is  now  injected  into  the  femoral  vein.  What 
conclusions  do  you  draw  from  the  result? 

202 


THE  PLETHYSMOGRAPH. 


203 


111111111  infill 


FIG.  61.     Tracing  of  volume  of  kidney  and  of  arterial  blood  pressure 
during  stimulation  of  the  splanchnic  nerve. 


204 


EXPERIMENTAL  PHYSIOLOGY. 


FIG.  62.     Tracing  of  volume  of  kidney  and  of  arterial  blood  pressure  during  asphyxia. 
slight  rise  in  blood  pressure  accompanied  by  marked  diminution  in  the  kidney  volume. 


Not 


THE  PLETHYMOGRAPH  205 

Curare  is  injected  into  the  femoral  vein  until  the  respirations 
cease  (see  p.  200).  Asphyxia  is  allowed  to  supervene  by  suspending 
the  artificial  respiration  (Fig.  62),  but  this  is  re-established  before 
the  final  fall  in  blood  pressure  sets  in.  What  evidence  does  the  result 
furnish  concerning  the  cause  of  the  asphyxial  rise  in  blood  pressure? 
(If  satisfactory  curare  is  not  available,  the  asphyxia  may  be  in- 
duced by  clamping  the  trachea.  The  results  are,  however,  less 
clear  because  of  the  respiratory  convulsions). 

Finally,  the  renal  nerves  are  cut,  and,  the  immediate  effect  on 
the  kidney  volume  having  been  observed  and  explained,  several  of 
the  foregoing  experiments  are  repeated.  How  do  you  explain  the 
alterations  in  the  results? 

The  anima1  is  killed  by  haemorrhage  while  the  various  tracings 
are  being  taken. 

In  one  or  other  of  these  demonstrations  the  opportunity  may 
present  itself  of  attempting  the  resuscitation  of  the  animal  by 
intra-arterial  transfusion  with  epinephrin.  To  effect  this 
a  cannula,  inserted  in  the  central  end  of  the  carotid  artery,  is  con- 
nected with  a  burette  containing  warm  isotonic  saline  solution, 
which  is  allowed  to  flow  into  the  artery.  Artificial  respiration  is 
also  performed  and  after  seme  saline  has  transfused  a  few  cubic 
centimetres  of  adrenalin  chloride  is  injected  into  the  tubing  which 
connects  the  artery  with  the  burette  and  the  thorax  is  vigorously 
massaged  over  the  region  of  the  heart.  In  a  successful  experiment 
the  blood  pressure,  recorded  from  the  carotid  on  the  opposite  side 
to  that  through  which  transfusion  is  being  made,  will  be  observed 
to  rise,  at  first  passively  because  of  the  thoracic  movements,  and 
later  because  of  resumption  of  the  heart  beats.  Once  these  have 
started  the  blood  pressure  quickly  recovers  and  the  cardiac  massage 
may  be  suspended.  Explain  the  mechanism  of  the  resuscitation 
and  particularly  how  the  epinephrin  acts.  Would  intravenous 
transfusion  be  of  any  avail  in  attempting  the  resuscitation  after 
complete  stoppage  of  the  heart  beat? 


CHAPTER  XXVII. 

PERFUSION  OF  THE  EXCISED  MAMMALIAN  HEART. 

If  a  solution  containing  certain  of  the  inorganic  constituents 
of  blood  plasma  and  saturated  with  oxygen  gas  be  perfused  under 
a  certain  pressure  through  the  coronary  arteries,  the  heart  will 
beat  with  perfect  regularity  for  several  hours  outside  the  body. 
This  surviving  heart  preparation  is  particularly  useful  for  investiga- 
tions of  the  influence  on  the  heart  of  variations  in  the  saline  con- 
stituents of  the  nutrient  fluid  and  of  the  effect  of  drugs.  The  nutrient 
fluid  is  caused  to  circulate  through  the  coronary  arteries  by  intro- 
ducing it  into  the  aorta,  where  it  closes  the  semilunar  valves  and 
is  forced  into  the  openings  of  these  arteries.  The  observation  also 
demonstrates  most  convincingly  the  remarkable  recuperative 
power  of  the  heart,  and  it  affords  evidence  that  resuscitation 
methods  should  be  persistently  applied  after  drowning  accidents 
and  when  death  has  occurred  from  other  forms  of  suffocation. 

The  most  convenient  apparatus  to  use  is  that  depicted  in  Fig.  63.  The  per- 
fusion  fluid  (Ringer-Locke's  or  Tyrode's)  is  contained  in  the  bottle  A,  and  it  is 
kept  constantly  saturated  with  pure  oxygen  by  bubbling  the  gas  through  it. 
The  fluid  then  passes  to  the  cannula  in  the  aorta  through  a  warming  device  which 
consists  of  a  wide  tube  surrounded  by  a  water  jacket  kept  at  the  desired  tempera- 
ture by  a  thermo-siphon  system,  as  shown  in  the  diagram.  In  order  that  the 
fluid  may  be  thoroughly  warmed  it  is  caused  to  flow  in  a  thin  film  on  the  walls  of 
the  tube  (B)  by  placing  in  this  a  somewhat  smaller  tube  (C)  closed  at  both  ends. 
Although  it  is  convenient  to  use  an  apparatus  in  which  the  free  end  of  the  cannula 
is  ground  on  its  outer  surface  so  as  to  fit  the  lower  end  of  the  inner  tube  of  the 
warmer — an  apparatus  devised  by  the  late  T.  G.  Brodie — the  simpler  apparatus 
devised  by  Gunn,  which  is  also  shown  in  the  figure,  is  perfectly  satisfactory. 
In  Brodie's  apparatus  a  thermometer  (T)  is  inserted  into  the  aortic  cannula 
through  a  side  tube;  in  Gunn's  apparatus  the  thermometer  is  made  to  serve  as  the 
inner  tube  of  the  warmer. 

The  heart  is  prepared  for  perfusion  as  follows:  A  rabbit  is  killed  by  a  blow 
on  the  back  of  the  head  and  is  immediately  laid  supine  on  the  table.  A  longi- 
tudinal incision  is  made  through  the  skin  of  the  thorax,  extending  for  a  short 
distance  on  the  abdomen.  The  skin  is  retracted  to  both  sides  of  the  incision 
and  the  abdomen  opened  at  its  upper  end.  One  blade  of  a  stout  pair  of  scissors 
is  then  passed  through  the  diaphragm  under  the  cartilages  of  the  ribs  on  one  side 

206 


PERFUSION  OF  THE  MAMMALIAN  HEART.  207 

A      f 


FIG.  63.     Apparatus  for  perfusion  of  the  mammalian  (rabbit)  heart.     The  apparatus  con- 
nected with  the  heating  device  is  that  of  Brodie.     Apparatus  of  Gunn  is  shown  in  insert. 

and  these  are  cut  from  below  upwards,  care  being  taken  to  keep  the  blade  away 
from  the  heart  and  lungs.  The  cartilages  are  similarly  cut  on  the  other  side  of  the 
sternum.  The  isolated  piece  of  sternum  is  bent  upwards  and  cut  across  at  the 
upper  end.  The  exposed  pericardium  is  picked  up  with  a  forceps  and  opened  with 


208  EXPERIMENTAL  PHYSIOLOGY. 

fine  scissors,  after  which  the  animal  is  placed  on  the  left  side,  so  as  to  expose  the 
structures  at  the  root  of  the  right  lung.  These  are  cut  through  and  the  operation 
is  repeated  on  the  other  side.  The  aorta  must  now  be  made  out  and  cut  across 
just  proximal  to  where  its  first  branch  (the  innominate)  comes  off,  after  which  the 
superior  vena  cava  is  cut  a  short  distance  from  the  auricle.  A  snip  is  made  in  the 
apex  of  the  right  ventricle,  using  a  small  sharp-pointed  scissors  for  the  purpose: 
this  is  to  permit  of  free  escape  of  the  fluid  from  perfusing  the  heart.  Finally  a 
thread  attached  to  a  packing  needle  is  inserted  in  the  inferior  vena  cava,  and  cau- 
tiously guided  upwards  so  that  it  emerges  from  the  superior  vena  cava.  The 
needle  is  unthreaded,  and  the  thread  tied  in  a  loop.  This  thread  is  introduced 
to  serve  as  a  guide  to  the  venae  cavae  into  which  later  a  tube  is  to  be  inserted. 
The  heart  is  removed,  by  cutting  the  inferior  vena  cava  below  the  thread,  and 
placed  in  a  dish  containing  cold  Locke's  solution.  Any  blood  remaining  in  the 
right  auricle  and  ventricle  is  then  washed  out  by  introducing  Locke's  solution 
from  a  large  pipette  through  the  superior  vena  cava.  The  special  cannula  is 
now  tied  into  the  aorta,  care  being  taken  that  no  air  bubbles  are  entrapped. 
(This  part  of  the  technique  is  more  conveniently  performed  with  Brodie's  appara- 
tus than  with  Gunn's,  but  it  is  perfectly  simple  using  the  latter).  A  bent  pin 
hook  is  passed  through  the  outer  coat  of  the  right  ventricle  and  a  thread  attached 
to  it  is  carried  over  a  pulley  to  a  heart  lever  arranged  to  write  on  a  drum.  A 
similar  hook  and  thread  may  also  be  attached  to  the  auricle  so  that  simultaneous 
tracings  of  auricle  and  ventricle  may  be  taken.  In  order  to  steady  the  heart  it  is 
well  to  pass  a  thread  through  the  apex  of  the  left  ventricle  and  tie  it  below  to  a 
glass  rod  fixed  to  a  stand. 

Demonstration  3. — Having  secured  a  tracing  of  the  heart  and 
noted  the  temperature  of  the  perfusion  fluid,  the  following  observa- 
tions may  now  be  made: 

1.  The  influence  of  changing  the  temperature  of  the  perfusion 
fluid.    This  can  best  be  done  by  adding  hot  or  cold  water  to  the 
copper  vessel  connected  with  the  water  jacket. 

2.  The  influence  of  the  local  application  of  heat  and  cold  in  the 
right  auricle.     To  demonstrate  this,  pass  a  thin-walled  glass  tube 
through  the  superior  and  inferior  venae  cavae  using  as  a  guide  the 
string  previously  placed  in  the  vessels.    The  upper  end  of  this  tube 
is  connected  by  rubber  tubing  with  a  funnel,  and  either  cold  or  hot 
water  is  made  to  flow  through  it  while  a  tracing  of  the  beat  is 
being  recorded.     The  temperature  of  the  perfusion  fluid  is  mean- 
while kept  exactly  constant  (cf.  Sherrington). 

3.  The  effect  produced  on  the  beat  by  increasing  the  relative 
proportion  of  the   calcium  or  potassium   in   the   perfusion   fluid. 
This  is  very  conveniently  accomplished  in  the  Brodie  apparatus 
by  closing  one  of  the  side  tubes  on  the  inflow  tube  leading  to  the 


PERFUSION  OF  THE  MAMMALIAN  HEART  209 

upper  end  of  the  warmer  with  rubber  tubing  through  the  wall  of 
which  is  inserted  the  needle  of  a  small  hypodermic  syringe  con 
taining  the  solution.  For  more  continuous  addition  of  greater 
dilutions  of  the  foreign  solution  the  side  tube  may  be  connected  with 
a  burette.  In  Gunn's  apparatus  a  Y  tube  is  provided  for  these 
operations.  By  thus  injecting  the  foreign  solution  at  a  distance 
from  the  heart  it  is  mixed  thoroughly  with  the  perfusion  fluid  and 
is  properly  warmed  before  the  heart  is  reached.  Observations  should 
be  made  using  first  of  all  a  few  c.c.  of  a  1%  solution  of  calcium 
chloride.  When  the  beat  becomes  very  small  and  the  ventricle  is 
almost  in  calcium  rigor  (see  p.  70)  inject  a  few  cc.  of  a  1%  solution  of 
KC1.  If  the  beat  does  not  become  restored  to  the  normal  in  a  few 
minutes  or  so,  inject  a  little  more  KC1  solution.  Then  add  still 
more  KC1  until  the  heart  again  almost  comes  to  a  standstill  (in 
diastole,  p.  57),  when  it  may  again  be  restored  by  injecting  CaCLj 
solution.*  It  is,  of  course,  evident  that  this  observation  does  not 
in  itself  prove  that  the  two  cathions  are  mutually  antagonistic  to 
each  other.  To  prove  this  it  would  be  necessary  to  show  that 
without  the  addition  of  the  antagonistic  cathion  the  beat  is  much 
more  slowly  restored. 

4.  The  effect  of  alteration  of  the  H-ion  concentration  of  the 
perfusion  fluid.    This  is  done  by  cautiously  adding,  by  the  above 
procedure,  0.9  per  cent,  solution  of  NaCl  containing  either  some 
HC1  or  some  NaOH. 

5.  The  effect  of  epinephrin.    For  this  purpose  about  1  c.c.  of  a 
0.002  per  cent,  solution  of  adrenalin  chloride  solution  should  give 
definite  results. 

6.  The  effect  produced  by  applying  a  tetanising  electric  current 
to  the  ventricle.     Whenever  the  fibrillation  becomes  marked  dis- 
continue the  stimulation  and  see  whether  the  normal  beat  becomes 
restored  by  continuing  the  perfusion.     Observe  carefully  the  be- 
haviour of  the  auricles. 

It  is  usually  necessary  to  employ  more  than  one  heart  for  all 
of  the  above  observations.  Sometimes,  however,  all  can  be  done 
on  one  preparation. 

*It  is  not  possible  to  state  precisely  what  amount  of  the  two  solutions  should 
be  used,  because  this  will  vary  with  the  rate  of  the  main  perfusion.  It  may  be 
necessary  to  repeat  the  observations  several  times  before  the  effects  are  obtained. 


CHAPTER    XXVIII. 

MEASUREMENT  OF  THE  BLOOD  FLOW  THROUGH  THE 
HANDS    AND    FEET,    BY    THE    CALORIMETRIC 
METHOD  OF  G.  N.  STEWART. 

ELECTROCARDIOGRAPHY 

Because  of  their  relatively  great  exposed  surfaces  the  hands, 
and  to  a  lesser  degree  the  feet,  quickly  give  off  heat  to  their  en- 
vironment. They  are  excellent  radiators.  The  muscles  of  these 
parts  when  at  perfect  rest,  contribute  but  a  very  small  quota  to 
this  heat,  most  of  which  therefore  is  carried  to  them  by  the  blood 
from  other  parts  of  the  body.  From  these  considerations  it  follows 
that  the  amount  of  heat  given  out  in  a  given  time  must  be  pro- 
portional to  the  amount  of  blood  flow,  or  expressed  in  precise 
terms:  the  amount  of  heat  given  off  in  calories,  divided  by  the 
difference  in  temperature  between  the  blood  flowing  to  and  away 
from  the  part  equals  the  volume  flow  of  blood  in  cubic  centimetres.* 

If  Q  be  the  grammes  of  blood  per  minute,  H  the  gram  calories 
in  m  minutes,  T  the  temperature  of  the  blood  entering  the  hand  and 
T'  that  of  the  blood  leaving  it,  S  being  the  specific  heat  of  blood  then : 

_         H  1 

Q==  m(T-T')  T" 

The  calories  are  measured  by  placing  the  hand  in  a  water 
calorimeter;  the  temperature  of  the  entering  blood  may  be  taken, 
as  that  under  the  tonguef  and  the  temperature  of  the  leaving 
blood  T',  as  the  mean  temperature  of  the  calorimeter  during  the 
observation. 

The  calorimeter  (see  Fig.  64)  consists  of  a  tinned  inner  copper  vessel  capable 
of  holding  somewhat  over  3000  c.c.  of  water.  This  vessel  is  placed  within  a  wider 
vessel,  the  space  between  the  two  being  packed  with  broken  cork.  To  the  open 
upper  end  of  the  inner  vessel  is  soldered  a  lid  of  copper  with  a  hole  cut  in  it 
towards  one  side  of  the  centre  and  large  enough  and  shaped  so  as  to  allow  the 

*A  small  or  gram  calorie  is  the  amount  of  heat  required  to  raise  the  tempera- 
ture of  1  gm.  of  water  through  1°  C. 

fBecause  of  the  liability  of  the  mouth  temperature  to  vary,  it  is  more  accurate 
to  take  for  T  the  rectal  temperature  less  0.5°  C. 

210 


BLOOD  FLOW  IN  MAN. 


211 


hand  to  pass  into  the  vessel.  About  an  inch  beyond  the  edges  of  this  hole  a 
strip  of  copper,  about  1  inch  wide,  is  soldered  at  right  angles  to  the  lid.  Besides 
the  hand-hole,  and  on  the  opposite  side  of  the  centre,  three  small  circular  holes 
are  made  in  the  lid  each  about  one  inch  in 
diameter  and  provided  with  a  copper 
tube  of  similar  diameter,  projecting  up- 
ward. A  piece  of  insulating  cork  is  cut  so 
as  to  form  a  lid  large  enough  to  fit  the 
outer  vessel,  and  holes  are  made  in  it  to 
fit  the  tubes  round  the  openings  in  the 
copper  lid  of  the  inner  vessel.  After  fitting 
the  cork  cover  in  place,  it  is  covered  with 
varnish.  The  three  small  holes  are  used, 
one  of  them  for  a  thermometer,  and  the 
others  for  long  feathers  to  serve  as 
stirrers.  A  piece  of  thick  saddler's  felt 
is  cut  to  fit  the  hand  opening  in  the  lid. 
Several  collars  of  the  same  material  are 
also  cut,  1  inch  wide,  and  of  various  sizes 
to  fit  wrists  of  different  sizes.  The  felt 
lid  and  collars  rest  on  the  copper  ledge 
between  the  head  opening  and  the  ridge 
of  copper.  A  thermometer  with  a 
scale  which  reads  between  0°  C.  and  50° 
C.  divided  into  l/10ths  is  sufficiently 
accurate.  By  using  a  telescope  the 
temperature  can  be  read  to  l/50th  or 
I/ 100th  of  a  degree. 

Besides  the  calorimeter,  a  large  bath 
of  20  or  30  litres  capacity  (garbage  can) 
is  necessary.  It  is  also  convenient  to  have 
an  adjustable  stool  (like  a  music  stool) 
on  which  to  place  the  calorimeter. 

Demonstration  4.— To  make 
the  measurement,  the  first  step 
is  to  draw  a  line  with  a  fat  pencil 
on  the  skin  at  the  lower  border  of 
the  styloid  process  of  the  ulna  of 
the  hand  chosen  for  observation. 
A  felt  collar  of  proper  size  is  then 
applied  to  the  wrist  with  its  lower 

border  corresponding  to  the  pencil  line,  and  a  second  line  is  drawn 
on  the  skin  opposite  the  upper  border  of  the  collar.  This  upper  line 
will  serve  as  a  mark  to  show  that  the  hand  is  not  changed  in  position 


FIG.  64.     Stewart's  Calorimeter. 


212  EXPERIMENTAL  PHYSIOLOGY. 

while  in  the  calorimeter.  The  hand  of  the  subject,  who  is  sitting 
on  a  high  chair,  is  then  placed  in  water  at  about  30-32°  C.  contained 
in  the  large  bath  (the  temperature  of  the  water  is  taken  by  an 
ordinary  thermometer)  and  it  is  left  there  for  ten  minutes,  or  so,  in 
order  that  the  skin  and  other  tissues  of  the  hand  may  be  brought 
to  the  same  temperature  as  the  water.  By  so  doing,  conditions 
are  established  which  are  analagous  to  those  which  would  exist  if 
the  blood  vessels  were  alone  suspended  in  the  water  bath.  The 
opposite  hand  is  covered  with  a  glove,  or  placed  in  the  pocket,  so 
that  it  may  not  become  cooled  and  so  cause  reflex  vaso-constric- 
tion  in  the  observed  hand.  While  the  hand  is  being  brought 
to  the  correct  temperature,  3,000  c.c.  of  water  is  removed  from 
the  large  bath  and  placed  in  the  calorimeter,  the  hand  opening 
of  which  is  then  closed  by  the  felt  lid.  The  water  is  occasionally 
stirred  by  the  feathers,  the  thermometer  is  placed  in  position,  and 
the  telescope  adjusted  so  that  an  exact  reading  of  the  temperature 
may  be  taken. 

When  the  ten  minutes  is  up,  the  hand  is  withdrawn  from  the 
bath,  the  wrist  quickly  wiped  dry  with  a  towel,  the  hand  with  the 
fingers  extended  carefully  passed  through  the  hand  opening  into 
the  water  in  the  calorimeter,  and  the  subject  instructed  to  keep  the 
fingers  abducted  and  extended  and  not  to  move  them.  He  must 
also  be  warned  not  to  touch  the  thermometer.  The  felt  collar  is 
placed  round  the  wrist  and  the  height  of  the  calorimeter  is  adjusted 
so  that  the  subject  does  not  require  to  strain  his  body  in  order  to 
keep  the  hand  in  the  correct  position  (or  with  the  upper  skin  line 
at  the  edge  of  the  felt  collar). 

The  observer  sits  on  a  low  stool  behind  the  subject,  and  having 
noted  the  time,  and  stirred  the  water  in  the  calorimeter,  proceeds 
to  record  the  temperature.  The  stirring  is  maintained  throughout 
the  observation,  which  lasts  10  minutes,  and  the  thermometer  is 
read  every  2  minutes.  When  time  is  up,  the  felt  collar  is  removed, 
the  hand  carefully  withdrawn,  and  the  hand  opening  covered  by 
the  felt  lid.  It  is  necessary  to  observe  the  temperature  in  the 
calorimeter  for  a  further  period  of  10  minutes,  with  constant  stirring, 
so  as  to  determine  the  extent  to  which  it  is  losing  heat  to  the  air 
(the  self-cooling  of  the  calorimeter). 

The  volume  of  the  hand  is  determined  by  placing  it,  while  still 


BLOOD  FLOW  IN  MAN.  213 

wet,  in  water  which  completely  fills  a  lipped  thick-walled  beaker  of 
suitable  size.  The  hand  displaces  an  equal  volume  of  water,  which 
overflows  into  a  basin  in  which  the  beaker  is  standing.  When  no 
more  water  overflows,  the  hand  is  slowly  withdrawn,  and  water 
is  added  from  a  graduate  to  the  beaker  until  it  is  again  full;  the 
amount  of  water  required  gives  the  volume  of  the  hand. 

The  temperature  of  the  mouth  or  rectum  is  finally  taken  and 
the  temperature  of  the  room,  read  from  a  thermometer  hanging 
from  the  chair  on  which  the  subject  sits,  recorded. 

To  apply  the  above  formula  to  calculate  the  blood  flow  it  is  necessary  to 
introduce  several  corrections  to  allow  for  differences  in  the  specific  heats  of  the 
hand  tissues,  of  the  metal  of  the  calorimeter  and  of  water.  These  corrections  are 
expressed  as  the  water  equivalents  of  the  hand  and  calorimeter.  The  water 
equivalent  of  the  calorimeter  is  determined  experimentally  for  each  calorimeter,, 
and  for  one  of  the  above  dimensions  will  be  about  100  c.c.  The  water  equivalent 
of  the  hand  is  obtained  by  multiplying  its  volume  by  0.8,  this  factor  being  the 
product  of  the  specific  gravity  and  the  specific  heat  of  the  hand. 

Suppose  in  an  experiment  that  the  temperature  of  the  calorimeter  during  an 
observation  lasting  10  minutes  had  risen  from  31°  C  to  31.5°  C  and  the  self-cooling 
of  the  calorimeter  during  the  subsequent  10  minutes  was  0.1°  C,  the  mouth 
temperature  being  37.5°  C.  and  the  volume  of  the  hand  450  c.c.,  then  (applying 
the  above  equation) : 

(3000+100+360)c.c.X(0.5+0.1)°C      10*_ 

37.5-31.25f  (    9   = 

The  measurement  should  now  be  repeated  under  the  following 
conditions: 

1.  When  the  opposite  hand,  instead  of  being  carefully  pro- 
tected from  cooling,  is  placed  in  cold  water.  A  marked  curtail- 
ment of  blood  flow,  due  to  reflex  vaso-constriction,  will  be  observed. 
This  observation  may  be  made  in  continuation  of  the  previous  one, 
i.e.,  the  unobserved  hand  kept  covered  for  10  minutes  and  then 
placed  in  cold  water  for  the  next  10  minutes.  It  is  particularly 
important  in  these  observations  to  read  the  calorimeter  temperature 
at  frequent  intervals,  because  the  vaso-constriction  that  is  im- 
mediately induced  gives  place  later  to  a  dilatation,  even  while 
the  opposite  hand  is  still  in  the  cold  water.  The  blood-flow  result 

*This  is  the  reciprocal  of  the  specific  heat  of  blood. 

fThis  is  the  mean  temperature  in  the  calorimeter  during  the  observation 

(36  9) 
of  the  hand  ---— - -8.2 


214  EXPERIMENTAL  PHYSIOLOGY 

for  each  two  minutes  should  be  plotted  on  coordinate  paper  to 
show  this  phenomenon. 

2.  After  the  hand  and  arm  have  been  used  to  perform  work, 
such  as  dumb  bell  exercise,  until  almost  fatigued. 

ELECTROCARDIOGRAPHY. 

Demonstration  4a. — Electrocardiography. — The  electro- 
cardiograph is  essentially  a  very  sensitive  galvanometer.  A  fibre 
of  finely  spun  glass  coated  with  a  film  of  silver  to  render  it  elec- 
trically conductive  is  suspended  between  the  poles  of  a  powerful 
electromagnet.  A  current  passing  through  the  fibre  or  string,  as 
it  is  termed,  causes  a  deflection  of  the  string  which  varies  with  the 
direction  of  the  current.  When  the  base  of  the  heart  is  relatively 
negative  to  the  apex  the  current  is  directed  upwards,  when  the 
apex  becomes  negative  the  current  passes  downwards  through  the 
string. 

By  means  of  an  arc  light  and  a  series  of  lenses  a  highly  magnified 
shadow  of  the  string  is  cast  upon  a  moving  photographic  plate 
which  descends  at  the  desired  speed  in  a  carrier  contained  within 
the  camera  box.  In  this  way  the  movements  of  the  string  are 
recorded. 

The  arc  lamp  having  been  lighted  and  the  shadow  of  the  string 
focussed  upon  the  scale  situated  on  the  front  of  the  camera,  the 
observed  person  is  seated  in  the  chair  with  each  hand  and  a  foot 
placed  in  the  respective  electrode  basins.  The  key,  A,  should  be 
in  the  short  circuit  position  and  the  key  B  at  "off"  before  the 
subject  is  connected  to  the  electrodes.  (See  Fig.  64a).  The  magnet 
should  be  now  excited  by  turning  on  the  house  current  and  the 
current  of  the  standard  cell  thrown  into  the  circuit  by  closing  the 
battery  switch.  The  current  of  the  standard  cell  serves  two 
purposes,  to  compensate  for  the  skin  current  and  to  standardize 
the  excursions  of  the  string.  The  electrode  switch  E  is  next  adjusted 
for  the  particular  lead  from  which  it  is  desired  to  obtain  a  record. 
The  switch  B  may  now  be  turned  to  " patient"  and  the  switch  A 
turned  from  the  short-circuit  position  to  1/100.  A  fraction  of  the 
current  from  the  subject  is  now  passing  through  the  string  and, 
though  the  cardiac  deflections,  if  seen  at  all,  will  be  very  minute, 
the  string  moves  from  the  zero  point  and  takes  up  a  new  position. 


BLOOD  FLOW  IN  MAN 


215 


This  change  in  the  position  of  the  string  is  due  to  skin  currents  and 
must  be  compensated  for.  The  current  of  the  standard  cell  which 
is  in  the  opposite  direction  is  used  for  this  purpose ;  the  compensator 
C  is  therefore  turned  until  sufficient  current  has  entered  the  cricuit 


G  O  O 


0!0 


216  EXPERIMENTAL  PHYSIOLOGY. 

to  bring  the,  string  back  to  its  original  position.  The  switch  A  is 
next  turned  to  1/10  and  finally  to  0,  any  movement  of  the  string 
from  zero  being  compensated  for  each  time.  The  skin  current  is 
now  fully  compensated  for  and  the  cardiac  deflections  are  more 
pronounced. 

In  order  that  all  electrocardiograms  may  be  compared  one  with 
another,  the  sensitivity  of  the  string  must  be  standardized  so  that 
a  given  strength  of  current  will  produce  a  certain  magnitude  of 
deflection.  The  standard  used  is  that  of  Einthoven — a  deflection 
of  1  centimetre  for  a  millivolt  of  current.  The  switch  A  is  turned 
to  the  left  from  0  to  1.  One  millivolt  derived  from  the  standard 
cell  is  now  passing  through  the  string  and  causes  it  to  be  deflected 
to  an  extent  which  is  dependent  upon  the  sensitivity  of  the  string. 
With  the  aid  of  the  scale  on  the  front  of  the  camera  box  the  magni- 
tude of  the  deflection  is  measured.  If  it  is  less  than  1  c.m.  the 
string  is  not  sensitive  enough  and  should  be  slackened.  This  is 
accomplished  by  turning  the  mill-headed  screw  above  the  fibre 
case  to  the  right,  i.e.,  in  the  direction  of  the  arrow  marked  thereon. 
If  the  deflection  is  more  than  1  c.m.  the  string  is  two  sensitive  and 
should  be  tightened  by  turning  the  milled  head  to  the  left. 

The  deflections  of  the  string  are  now  standardized  and  a  record 
may  be  taken.  The  plate  is  exposed  by  removing  its  sliding  cover, 
the  camera  slit  is  opened  and  the  carrier  released.  As  the  plate 
descends  behind  the  lens  of  the  camera  the  string  movements  are 
recorded.  The  time  in  1/50  of  seconds  is  indicated  by  upright 
lines  marked  upon  the  plate  by  means  of  a  revolving  wheel  placed 
between  the  source  of  light  and  the  string.  Horizontal  lines  repre- 
senting 1/10  millivolt  are  marked  upon  the  plate  by  means  of 
lines  engraved  upon  the  surface  of  the  camera  lens.  A  record 
should  be  taken  from  each  of  the  three  leads. 

Each  student  will  be  provided  with  a  record  which  he  should 
study  with  regard  to  the  following  points — 

1.  Identify  the  various  waves  upon  the  tracings  denoting  each 
by  its  appropriate  letter. 

2.  Measure  the  length  of  the  P-R  interval.     What  may  an 
examination  of  this  interval  tell  you  concerning  the  heart's  action? 

3.  Paste  the  electrocardiogram  in  your  note-book   and  draw 
beneath  it  a  jugular  pulse  tracing  and  an  intraventricular  pressure 


BLOOD  FLOW  IN  MAN.  217 

curve  so  as  to  synchronize  accurately  the  various  cardiac  events 
represented  in  the  three  tracings. 

4.  Determine  in  millivolts  the  manifest  value  of  the  potential 
change  occurring  during  the  production  of  the  R  wave  in  lead  III. 

5.  Determine  the  direction  of  the  electrical  axis  during  the 
production  of  the  R  wave. 

6.  Draw  a  diagram  showing  the  course  of  the  cardiac  action 
current  and  the  movement  of  the  string  during  the  production  of  the 
P  wave. 


CHAPTER    XXIX. 

LYMPH  FORMATION. 

Demonstration  5. — A  large  dog  is  given  a  meal  containing  an 
excess  of  fat  (lard)  several  hours  prior  to  the  experiment.  After 
anaesthetising  with  morphine  and  ether  and  inserting  tracheal  and 
carotid  cannulae  the  thoracic  duct  is  exposed  as  it  enters  the  left 
subclavian  vein  at  the  root  of  the  neck.  This  operation  is  rather 
difficult  and  should  be  performed  as  follows:  after  extending  the 
incision  through  skin  and  subcutaneous  tissue  down  to  the  sternal 
notch,  the  sterno  mastoid  and  sterno  hyoid  muscles  are  cut  as  low 
down  as  possible  on  the  left  side  and  reflected  upwards.  The  ex- 
ternal jugular  vein  is  then  followed  downward  till  it  joins  the 
subclavian,  which  is  traced  inwards  to  its  union  with  the  internal 
jugular.  In  the  fork  at  the  union  of  these  two  veins  the  thoracic 
duct  is  sought  for  by  very  careful  dissection  (see  Fig.  65),  great 
care  being  exercised  so  as  not  to  wound  the  pleura  which  lies 
immediately  beneath  the  vein.  Just  before  entering  the  vein  the 
thoracic  duct,  curving  forwards  and  outwards,  is  joined  by  the 
somewhat  smaller  neck  lymphatic.  The  duct  is  rendered  visible 
by  the  white  creamy  fluid  it  contains,  the  neck  lymphatic  being 
similarly  injected  to  a  lesser  degree.  (Usually  it  is  advisable  to 
ligate  the  neck  lymphatic,  but  when  possible  a  cannula  should  be 
placed  in  it  (pointing  upwards)  since  the  lymph  flow  from  this 
lymphatic  does  not  behave  exactly  like  that  from  the  thoracic 
duct).  To  introduce  the  cannula  into  the  thoracic  duct  two  liga- 
tures are  placed  under  the  latter,  the  one  next  the  subclavian  vein 
being  tied,  and  a  slit  is  made  with  a  fine  pointed  sharp  scissors  in 
the  duct;  the  edge  of  the  slit  is  then  caught  in  a  fine  pair  of  forceps 
and  a  glass  cannula  (with  an  outside  diameter  of  about  1/32  inch) 
inserted  and  tied  in  by  the  second  ligature.  If  the  creamy  lymph 
escapes  so  freely  from  the  slit  in  the  duct  that  it  fills  the  wound 
its  flow  should  be  controlled  by  pulling  gently  on  the  free  ligature. 
Usually  a  certain  amount  of  lymph  flow  is  desirable  since  it  facili- 

218 


LYMPH  FORMATION. 


219 


FIG.  65.     Dissection  necessary  for  exposure  of  thoracic  duct  and  neck  lymphatic.     Ligatures 
are  placed  around  these  structures.     (After  Jackson). 


220  EXPERIMENTAL  PHYSIOLOGY. 

tates  insertion  of  the  cannula.  It  should  be  remembered  that  the 
lymph  clots  readily,  and  if  this  occurs  in  the  neck  of  the  cannula, 
the  clot  will  require  to  be  broken  up  by  means  of  a  fine  hair.  The 
cannula  is  connected  by  a  short  piece  of  flexible  rubber  tubing  with  a 
bent  glass  tube,  from  the  end  of  which  the  lymph  is  allowed  to  drop. 

A  cannula  is  also  inserted  in  the  femoral  vein  and  connected 
with  a  burette. 

There  are  two  types  of  experiment  which  may  be  demonstrated 
on  lymph  flow.  One  of  these  concerns  the  stimulating  effect  of 
certain  chemical  substances  when  injected  into  the  general  circula- 
tion— the  lymphagogues — and  the  other,  the  effect  of  alterations  of 
the  circulatory  conditions  in  the  intestines  and  liver. 

The  lymphagogues  are  of  two  classes,  saline  and  colloid.  To 
illustrate  the  former  a  strong  solution  of  glucose  (20  per  cent.)  is 
injected  intravenously  a  few  c.c.  at  a  time  until  an  increase  in  the 
number  of  drops  of  lymph  is  produced.  The  amount  of  injection  is 
then  increased.  If  the  neck  lymphatic  flow  is  also  being  observed, 
particular  regard  should  be  given  as  to  whether  it  behaves  similarly 
to  that  of  the  thoracic  duct.  Repeat  the  experiment,  using  a  10  % 
solution  of  sodium  chloride.  Explain  the  results. 

In  the  foregoing  experiment  it  will  be  observed  that  the  arterial 
blood  pressure  either  remains  unaltered  or  rises  slightly.  To 
illustrate  the  colloid  lymphagogues,  small  quantities  of  a  solution 
of  commercial  peptone  are  injected.  Note  that  besides  affecting 
the  lymph  flow  there  is  a  decided  drop  in  arterial  blood  pressure. 
(Care  must  be  taken  not  to  allow  this  to  reach  the  danger  limit). 
Explain  the  result. 

Finally  it  may  be  shown  that  certain  drugs  and  hormones  also 
act  as  lymphagogues.  To  illustrate  this,  pituitrin  may  be  used 
(1  c.c.  for  a  dog  of  average  size,  8  kgm.). 

The  influence  of  circulatory  changes  in  the  splanchnic  region 
may  be  illustrated  as  follows:  after  opening  the  abdomen  in  the 
linea  alba  a  loose  ligature  is  placed  around  the  portal  vein  near 
the  hilus  of  the  liver.  When  the  normal  rate  of  lymph 
flow  (from  both  ducts)  has  been  ascertained  the  vein  is  closed  by 
pulling  on  the  ligature;  a  decided  increase  in  flow  is  observed. 
If  the  ligature  be  tightened  for  long  the  lymph  will  become  turgid 
with  blood.  How  do  you  explain  the  results? 


LYMPH  FOUNDATION  221 

Finally  the  lymphatics  which  accompany  the  portal  vein  are 
ligated.  This  is  readily  done  by  separating  the  vein  by  blunt  dis- 
section from  the  accompanying  structures,  which  are  then  mass 
ligated.  A  loose  ligature  is  next  placed  around  the  inferior  vena 
cava  just  above  the  diaphragm,  by  making  an  opening  at  the 
posterior  end  of  the  6th  or  7th  intercostal  space  on  the  right  side, 
prying  the  ribs  apart  with  a  strong  pair  of  retractors  (meanwhile 
maintaining  artificial  respiration)  and  threading  the  ligature 
around  the  vein  by  a  long  aneurysm  needle.  After  applying  the 
ligature,  the  opening  in  the  thorax  should  be  closed  by  artery  for- 
ceps, when  it  will  often  be  found  that  artificial  respiration  can 
be  discontinued.  Having  observed  the  rate  of  lymph  flow  the 
ligature  is  tightened  for  a  few  moments.  Is  the  effect  similar  to 
that  of  the  previous  experiment?  How  is  it  explained? 

SECRETION    OF    URINE 

Demonstration  5a.— The  experiment  may  be  performed  on  a 
dog  or  cat  anaesthetized,  preferably  with  urethane  (2  grams  per 
kilo  given  by  stomach  with  an  abundance  of  water).  Insert  a 
canula  in  trachea,  a  canula  in  femoral  vein  for  injection,  and  a 
canula  in  the  right  carotid  artery  for  recording  blood  pressure 
with  mercury  manometer.  Expose  the  left  vagus  nerve  and 
arrange  for  stimulating  the  peripheral  end.  The  secretion  of 
urine  is  to  be  observed  by  counting  the  drops  which  issue  from  a 
canula  inserted  into  the  urinary  ducts.  In  the  case  of  the  dog 
the  abdominal  cavity  may  be  opened  and  a  slender  canula 
inserted  into  one  of  the  ureters.  In  the  case  of  the  cat  a  large 
canula  may  be  inserted  into  the  urethra  by  means  of  an  incision 
made  just  cephalad  of  the  pubis.  The  bladder  will  empty  itself 
through  this  canula,  and  if  care  is  taken  that  the  urethral  canula 
does  not  become  blocked  all  urine  flowing  from  the  ureters  will 
pass  through  this  canula  without  accumulating  in  the  bladder. 

Do  not  attempt  to  repeat  the  observations  because  the  secretion 
will  not  continue  indefinitely.  Observe  the  following: 

(A)   The  Effect  of  Blood  Pressure  upon  the  Secretion  of  Urine. 

1.  Determine  the  normal  blood  pressure  and  rate  of  urine  flow. 

2.  Inject  0.5  c.c.  1,  10,000  Adrenin  into  the  femoral  vein. 


222  EXPERIMENTAL  PHYSIOLOGY. 

(a)  What  is  the  effect  on  blood  pressure;  on  diuresis? 

(b)  How  can  these  effects  be  correlated? 

3.  Stimulate  the  vagus. 

(a)  What  is  the  effect  on  blood  pressure;  on  diuresis? 
(E)   The  Effect  of  the  Chemical   Composition  of  the  Blood  upon 
the  Secretion  of  Urine. 

4.  Inject  15  c.c.  of  a  1%  solution  of  urea  into  the  femoral  vein. 

(a)  What  is  the  effect  on  diuresis? 

(b)  Can  this  effect  be  attributed  to  changes  in  blood  pressure? 

5.  After  the  diuresis  returns  to  normal  inject  50  c.c.  of  a  warm 
isotonic  salt  solution  slowly  into  the  femoral  vein. 

(a)  What  is  the  effect  on  diuresis? 

(b)  Can  this  effect  be  attributed  to  changes  in  blood  pressure? 

(C)  The  Time  Interval  of  Urine  Secretion. 

Introduce  5  c.c.  of  a  saturated  solution  of  indigo-carmine  into 
the  vein.  Note  the  time  which  elapses  until  the  blue  colour  first 
appears  in  the  urine. 

(D)  Asphyxiation  of  Kidney. 

6.  Close  the  tracheal  cannula  with  the  finger  for  60  seconds. 

(a)  Note  and  explain  effect  upon  diuresis. 

(b)  Can  this  be  explained  by  the  changes  in  blood  pressure? 
The  operator  may  now  open  the  body  cavity  and  place  ligatures 

around  the  renal  arteries  and  veins  of  both  kidneys  and  around 
the  aorta  caudad  to  renal  arteries.  Look  for  rhythmic  movements 
of  the  ureters. 

7.  Close  aorta  below  renal  arteries. 

(a)  State  and  explain  effect  on  diuresis. 

8.  Close  the  renal  veins  by  pulling  up  on  the  ligatures  about 
them.    Do  not  check  the  renal  circulation  for  more  than  a  minute 
in  this  way. 

(a)  State  and  explain  effect  on  diuresis. 

9.  Close  the  renal  artery  by  pulling  up  on  the  ligatures  for  three 
minutes. 

(a)  What  is  the  effect  upon  diuresis? 

(b)  Explain. 

(c)  Does  the  kidney  recover  from  the  asphyxiation? 


CHAPTER  XXX. 

EXPERIMENTS  TO  DEMONSTRATE   THE  PUMPING 

ACTION  OF  THE  HEART  AND  THE  ACTION  OF 

THE  VALVES. 

Demonstration  6. — A  wide  glass  cannula  is  tied  into  the 
superior  vena  cava  of  the  excised  heart  of  a  dog  or  sheep  and  the 
cannula  connected  by  rubber  tubing  with  a  funnel.  A  glass  tube 
is  also  tied  into  the  pulmonary  artery,  the  upper  end  of  the  tube,  at 
a  distance  of  about  50  cm.  from  the  heart  end,  being  bent  double 
and  arranged  so  that  the  opening  lies  over  the  funnel  which  is 
connected  with  the  vena  cava.  The  inferior  vena  cava  is  tied  and 
the  preparation  and  tube  are  held  by  suitable  clamps  in  a  vertical 
position ;  water  is  poured  into  the  funnel  so  that  it  distends  the  right 
auricle  and  ventricle.  Some  of  the  water  escapes  through  cut 
vessels  (left  azygos  vein)  which  are  now  tied.  When  the  ventricle 
is  rhythmically  compressed  by  the  hand  the  water,  which  has  mean- 
while risen  in  the  pulmonary  tube  to  the  level  of  the  water  in  the 
funnel,  rises  higher  and  higher  with  each  compression,  and  remains 
up  between  them,  until  it  reaches  the  bend  and  flows  back  into  the 
funnel.  This  illustrates  the  circulation  of  the  blood  through  the 
heart. 

It  is  interesting  to  study  the  effect  produced  by  DAMAGING  THE 
SEMILUNAR  VALVE.  The  fluid  still  rises  in  the  tube  with  each 
compression,  but  leaks  back  into  the  ventricle  between  the  "beats". 
To  raise  the  fluid  in  the  tube  high  enough  so  that  it  overflows  into 
the  funnel  it  is  now  necessary  to  compress  the  ventricle  much  more 
rapidly.  This  illustrates  in  a  rough  way  how  the  heart  may  com- 
pensate for  a  valvular  inefficiency  by  more  energetic  action. 

The  OPERATION  OF  THE  TRicusPiD  VALVES  is  also  readily  shown 
by  removing  the  tube  and  cutting  away  most  of  the  right  auricle. 
When  the  ventricle  is  filled  the  water  flaps  are  floated  up  into 
position,  a  narrow  chink,  however,  remaining  in  the  centre.  This 
can  be  temporarily  closed  by  allowing  the  water  to  drop  in  the 

223 


224 


EXPERIMENTAL  PHYSIOLOGY. 


FIG.  66.     Gad's  arrangement  for  observing  the  action  of  the  cardiac  valves.  (After  Tigerstedt) 


HEART  PREPARATION.  225 

centre  of  the  chink;  following  each  drop  the  flaps  come  accurately 
together  because  the  waves  of  pressure  produced  by  each  drop 
are  reflected  onto  the  under  surface  of  the  flaps  from  the  walls  of  the 
ventricle.  What  significance  may  this  observation  have  in  con- 
nection with  the  mechanism  of  the  closure  of  the  valves  in  the 
normal  heart? 

To  illustrate  the  efficiency  of  the  tricuspid  valves,  ligate  the 
pulmonary  artery,  fill  the  ventricle  with  water,  and  hold  the  ven- 
tricle upside  down;  the  water  stays  in. 

The  operation  of  the  valves  can  be  very  clearly  shown  by  ob- 
serving them  through  windows  inserted  in  the  right  auricle  and 
pulmonary  artery.  This  is  known  as  GAD'S  HEART  PREPARA- 
TION. 

Demonstration  7. — The  general  arrangement,  using  an  ox 
heart,  is  shown  in  Fig.  66.  A  brass  tube  A  (40  cm.  diam.) 
closed  by  a  glass  window  at  one  end  and  with  a  narrow  tube  soldered 
into  its  side  is  tied  into  the  right  auricle,  and  another  similar,  but 
narrower  tube  B  (25  cm.  diam.)  into  the  pulmonary  artery.  The 
side  tube  of  A  is  connected  by  rubber  tubing  with  the  outflow  of 
an  irrigation  bottle,  to  the  mouth  of  which  leads  a  tube  from  B. 
Through  a  narrow  cut  in  the  apex  of  the  ventricle  a  brass  tube 
C  connected  at  its  free  end  with  a  rubber  bulb  and  having  a  side 
tube  closed  by  a  small  rubber  stopper,  which  is  pierced  by  water- 
proofed insulated  wires,  is  inserted  and  tied  in.  The  wires  are 
connected  with  a  small  electric  lamp  D  which  projects  into  the 
ventricle.  By  rhythmically  compressing  the  bulb  E,  to  simulate 
the  ventricular  contractions,  water  is  transferred  from  the  auricle 
to  the  pulmonary  artery,  and  with  each  pulsation  the  tricuspid 
and  semilunar  valves  can  be  very  distinctly  seen  to  open  and 
close  in  obeyance  to  the  pressure  changes. 


SECTION  VII. 

THE  DIGESTIVE  SYSTEM. 
CHAPTER   XXXI. 

THE  INNERVATION  OF  THE  SALIVARY  GLANDS. 

The  general  nature  of  THE  NERVE  CONTROL  OF  SECRETORY 
GLANDS  is  most  readily  studied  on  the  submaxillary  gland  of  the 
dog  or  cat.  The  responses  are  not  exactly  alike  in  the  two  animals, 
but  the  results  typify  glandular  innervation  in  general. 

Demonstration  8. — A  dog  is  anaesthetized  preferably  by 
.  urethane  (p.  72)  and  tracheal  and  carotid  cannulae  are  inserted. 
An  incision  is  made  along  the  inner  border  of  the  ramus  of  the  lower 
jaw  extending  from  the  mouth  to  the  angle  of  the  jaw.  The  digas- 
tric muscle  is  exposed  and  is  strongly  retracted  outwards  so  as  to 
expose  the  mylohyoid  muscle,  the  fibres  of  which  run  transversely 
to  the  wound.  The  hypoglossal  nerve  is  seen  extending  backwards 
behind  the  posterior  edge  of  the  mylohyoid.  A  probe  or  blunt 
dissector  is  pushed  under  the  latter  muscle  and  its  fibres  cut  in  the 
same  line  as  the  main  wound.  This  exposes  the  ducts  of  the  sub- 
maxillary  (and  sublingual)  glands  with  the  lingual  nerve  crossing 
them.  A  ligature  ,is  tied  on  this  nerveySew--  the  d-uc4s  and  the 

t.t.  -^-»t<>«^^|^^»v>A^p^ 

nerve  cut  peripheral  to  the  hgafture^after  which  it  is  traced  up  under 
the  ramus  of  the  jaw,  the  small  branch  which  arises  from  it  and 
proceeds  forwards  being  cut.  Just  above  where  this  branch  comes 
off  another  branch  passes  backwards  and  downwards  to  join  the 
ducts  a  short  distance  from  the 'place  of  crossing  of  the  lingual. 
This  is  the  chorda  tympani  nerve.  It  can  be  prepared  for  artificial 
stimulation  by  tying  a  second  ligature  round  the  lingual  nerve 
above  where  the  chorda  arises  and  cutting  above  the  ligature. 
By  holding  up  the  piece  of  lingual  by  the  two  ligatures  the  elec- 
trodes can  be  readily  applied  to  the  chorda.  ' '  / 

J        ^^  **4UC4LCZ4L  9*4O'CU'v>£u4 

Before  attempting  to  insert  a  cannula  in  Wharton's  duct  the 
chorda  should  be  stimulated  with  a  feeble  tetanizing  current  after 

226 


SECRETION  OF  SALIVA.  227 

placing  bull  dog  forceps  on  the  two  ducts  well  forward  of  the  point 
where  the  lingual  crosses  them.  This  causes  the  ducts  to  distend 
and  into  the  one  which  does  so  most  markedly  a  small  cannula  is 
inserted  by  the  same  manipulation  as  for  a  vein  (p:  8d). 

The  skin  wound  should  now  be  carried  back  and  the  sub- 
maxillary  gland  carefully  freed  by  blunt  dissection  from  the  neigh- 
bouring tissues,  care  being  taken  not  to  injure  the  veins.  The 
exposed  gland  should  be  kept  moist  with  warm^todke's  solution. 

The  cannula  is  connected  by  suitable  rubber  tubing  with  a  bent 
glass  tube  so  arranged  that  the  drops  of  secretion  may  fall  from  its 
free  end.  Having  ascertained  the  rate  of  secretion  (by  counting  the 
drops)  for  a  normal  period  of  one  minute  the  chorda  is  stimulated 
for  a  few  moments  with  a  feeble  interrupted  current.  When  the 
secretion  has  returned  to  normal,  stimulation  is  repeated  with  a 
stronger  current. 

The  relationship  between  the  response  and  the  strength  of  the 
stimuli  should  be  carefully  noted.  Those  near  the  preparation  can 
usually  see  that  the  gland  becomes  flushed  and  apparently  swollen 
by  the  stimulation,  this  effect  being  usually  most  pronounced  during 
the  first-applied  stimuli.  What  conclusions  are  warranted  from 
the  results?  The  observations  are  repeated  during  stimulation 
of  the  central  end  of  the  vago-sympathetic  in  the  neck. 

The  secretion  pressure  is  now  measured  by  connecting  the 
cannula,  by  moderately  thick-walled,  but  yet  flexible  tubing,  with  a 
mercury  manometer,  the  tubing  being  filled  with  physiological 
saline.  The  carotid  blood  pressure  is  also  observed,  and  it  is 
advantageous  to  arrange  the  writing  styles  of  the  two  manometers 
so  that  they  write  in  the  same  perpendicular  on  a  drum.  When  the 
chorda  is  stimulated  with  a  current  which  gives  a  maximal  secretion, 
the  pressure  in  the  duct  manometer  steadily  rises  until  it  overtops 
that  in  the  artery.  Explain  the  significance  of  this  result. 

The  manometer  is  now  removed,  and,  through  a  cannula  pre- 
viously inserted  in  the  femoral  vein,  10-15  mgm.  of  atropine  sul- 
phate dissolved  in  physiological  saline  is  injected.  When  the  drug 
has  developed  its  full  action  on  the  heart  (how  is  this  tested?)  the 
chorda  is  again  stimulated  with  a  maximal  current,  and  the  effect 
on  the  secretion  and  the  vascularity  of  the  gland  observed.  What 
has  been  the  action  of  the  atropine?  Of  what  significance  is  the 
experiment? 


CHAPTER  XXXII. 

THE  CONTROL  OP  THE  PANCREATIC  SECRETION. 
THE  SECRETION  OF  BILE. 

As  an  example  of  THE  CONTROL  OF  GLANDULAR  FUNCTION 
THROUGH  HORMONES  it  is  most  convenient  to  take  the  pancreas. 
The  hormone  for  this  gland  is  derived  from  the  duodenal  mucosa 
where  it  is  produced  by  the  action  of  the  acids  present  in  the  chyme 
on  a  constituent  of  the  epithelial  cells,  and  it  is  then  carried  to  the 
pancreas  by  the  blood. 

Demonstration  9. — An  anaesthetized  dog  that  has  been  starv- 
ed for  24  hours  is  prepared  for  registration  of  the  arterial  blood 
pressure,  and  a  cannula  is  inserted  in  the  femoral  vein.  The  abdo- 
men is  opened  in  the  linea  alba  and  the  duodenum  along  with  the 
adherent  pancreas  pulled  out  of  the  wound.  The  lower  (and 
larger)  duct  of  the  pancreas  is  then  exposed,  and  a  ligature  placed 
under  it.  The  position  of  this  duct  is  indicated  approximately  by  a 
small  lobe  of  pancreas,  accompanied  by  bloodvessels,  which  extends 
to  the  duodenum  at  a  distance  of  about  20-25  mm.  above  the 
point  where  the  head  of  the  pancreas  leaves  the  duodenum.  It 
must  be  remembered  that  the  duct  begins  branching  very  close  to 
its  insertion  into  the  duodenum  so  that  only  a  small  piece  of  it  can 
be  dissected  free.  To  insert  a  cannula  into  the  duct  the  duodenum 
is  opened  by  a  longitudinal  incision  along  its  free  border  opposite 
the  duct,  the  opening  of  which  is  then  visible  in  the  centre  of  a  small 
papilla  of  somewhat  paler  tissue  than  the  remainder  of  the  mucosa. 
A  blunt  probe  should  be  inserted  into  the  duct  and  gently  guided 
along  it  so  as  to  ascertain  the  exact  direction  of  the  duct  and  the 
position  of  the  first  branch.  As  the  probe  is  withdrawn  a  suitable 
cannula  with  a  well-marked  neck  is  inserted  and  tied  in  position 
by  the  ligature  previously  applied  outside  the  duct.  A  cannula  is 
now  placed  in  the  common  bile  duct,  which  is  readily  found  accom- 
panying the  portal  vein. 

228 


SECRETION  OF  PANCREATIC  JUICE  AND  BILE.  229 

The  following  observations  on  the  secretions  from  the  two  ducts 
are  now  made. 

1.  Having  observed  the  normal  rate  of  secretion,  a  small  piece 
of  cotton  soaked  in  a  weak  solution  of  hydrochloric  acid  (less  than 
1%)  is  placed  in  the  duodenum.     Whenever  the  secretion  from  the 
pancreatic  duct  becomes  decidedly  increased   (not  an  invariable 
result)   the  cotton  is  removed,  and  the  duodenum  washed  with 
physiological  saline  rendered  faintly  alkaline  by  sodium  carbonate. 
Sometimes   an   increased   secretion   of   bile   occurs.     From   what 
sources  may  this  bile  be  derived?     What  experimental  steps  would 
you  suggest  in  order  to  ascertain  this? 

2.  The  exciting  influence  of  the  acid  might  of  course  be  due 
to  its  absorption  into  the  blood.     To  test  this  possibility  inject 
some  of  the  acid  into  the  femoral  vein.     A  negative  result  is  ob- 
tained even  when  massive  doses  are  injected. 

3.  Pieces  (about  2  feet  long)  of  the  upper  end  of  the  jejunum  and 
of  the  lower  end  of  the  ileum  are  then  removed,  by  cutting  between 
previously  applied  ligatures,  and  the  contents  washed  out  by  tap 
water.      Each  piece  is  then  slit  open  and  the  mucosa  scraped  off  by 
the  blunt  edge  of  a  scalpel  and  collected  in  separate  watch  glasses. 
One  half  of  each  scraping  is  thoroughly  ground  in  a  small  mortar 
with  fine  quartz  sand  and  about  30  c.c.  of  0.6  per  cent,  hydro- 
chloric acid  (2  c.c.  HC1  (Con)  in  100  c.c.  water.)     The  extracts  are 
filtered  through  fine  muslin  and  nearly  neutralised  (but  left  dis- 
tinctly acid  towards  litmus).    About  5  c.c.  of  the  extract  of  jejunum 
is  then  injected  into  the  femoral  vein  and  observations  made  on 
the  arterial  blood  pressure,  the  secretion  of  pancreatic  juice  and  the 
secretion  of  bile.     (Prior  to  this,  however,  the  cystic  duct  should 
have   been   tied   off.     Why?)     The   blood   pressure   usually   falls 
considerably  and  care  must  be  taken  so  to  regulate  the  rate  (and 
amount)  of  injection  that  the  fall  is  not  allowed  to  go  too  far. 
What  conclusions  regarding  the  mechanism  of  the  increased  secre- 
tion can  be  drawn  from  the  results?     To  obtain  satisfactory  results 
it  may  be  necessary  to  repeat  the  injection  using  double  the  amount 
and  injecting  more  quickly. 

The  observation   should   then   be  repeated   using  a   similarly 
prepared  extract  of  ileum.      A  much  feebler   response,  if   any  re- 


230  EXPERIMENTAL  PHYSIOLOGY. 

sponse  at  all,  is  observed,  but  the  fall  in  blood  pressure  is  as  pro- 
nounced as  before.     What  conclusions  do  you  draw  from  the  result? 

4.  Having  demonstrated  the  secretagoguary  action  of  the  duo- 
denal extract,  the  question  arises  as  to  the  general  nature  of  the  excit- 
ing substance.    The  remaining  portion  of  the  acid  extract  of  jejunum 
is  therefore  boiled  (in  faintly  acid  reaction)  and  filtered  through  thin 
filter  paper.     The  filtrate  is  found  to  be  still  active  when  injected. 
What  conclusions  do  you  draw?     Has  any  change  occurred  in  the 
vaso-depressor  effect?     The  secretion  of  bile  is  often  observed  to 
respond  to  the  injections  in  the  same  manner  as  the  pancreatic 
juice,  and  its  behaviour  therefore  should  be  carefully  watched. 

5.  Having  established,  by  these  experiments,  that  acid  extracts 
a  pancreatic  hormone  from  the  mucosa  (seeretin)  the  question  arises 
as  to  whether  the  hormone  is  present  therein  as  such  or  as  a  pre- 
cursor which  the  acid  activates.     To  throw  light  on  this  question, 
the  unextracted  half  of  the  mucosa  scrapings  is  ground  in  a  mortar 
with  quartz  sand,  and  0.9  per  cent,  sodium  chloride  solution,  and 
after  filtering  the  extract  through  muslin,  about  half  of  it  is  in- 
jected   intravenously.     The    result    is    negative.     The    remaining 
portion  of  the  extract  is  then  rendered  faintly  acid  with  HC1, 
boiled  and  filtered.     (3n  injection  a  slight,  but  yet  definite  increase 
usually  occurs  in  pancreatic  secretion.     What  conclusions  are  per- 
missible from  these  results? 

6.  Finally  the  influence  of  the  intravenous  injection  of  a  solution 
of  bile  salts  on  the  outflow  from  the  bile  duct  should  be  observed. 


CHAPTER  XXXIII. 

EXPERIMENT  ON  THE  NORMAL  SECRETION  OF 
SALIVA  AND  GASTRIC  JUICE. 

In  order  to  study  the  secretion  of  the  digestive  glands  in 
an  unaesthetized  normal  animal  it  is  necessary  by  surgical  methods 
to  establish  permanent  openings  or  fistulse  on  the  surface  of  the 
body,  through  which  the  secretions  may  escape.  This  method  has 
been  employed  with  great  profit  in  the  case  of  several  of  the  glands, 
the  general  nature  of  the  experiments  being  adequately  illustrated 
by  observation  on  the  parotid  gland  (representing  a  gland  with  a 
definite  duct)  and  the  stomach  (representing  a  gland  which  secretes 
directly  on  to  a  mucous  surface).  The  operations  necessary  to 
establish  the  fistula  are  performed  by  some  competent  assistant, 
and  the  operated  animals  are  carefully  tended  so  that  the  wounds 
heal  without  suppuration.  For  successful  observations  it  is 
furthermore  of  importance  that  the  animal  should  become  used  to 
the  person  who  is  to  demonstrate  the  experiments. 

The  Normal  Secretion  of  Saliva. 

METHOD  FOR  MAKING  FISTULA  OF  THE  PAROTID  GLAND. — A  dog  is  anaesthetised 
with  morphine  (morphine  hydrochloride  0.01  gm.  perkgm.  body  weight)  and  finally 
with  chloroform.  The  mouth  is  held  open  by  means  of  a  suitable  gag  and  the 
ductus  Stenonianus  located  (on  the  mucosa  of  the  cheek  opposite  the  second 
molar  tooth).  A  small  blunt  probe  is  pushed  into  the  duct  and  the  mucous  mem- 
brane around  it  sponged  with  sterile  surgical  gauze.  A  circular  incision  is  then 
made  through  the  mucosa  around  the  duct,  the  area  of  the  circle  being  a  little  less 
than  one  sq.  cm.  It  will  probably  be  necessary  at  this  stage  to  suspend  further 
operating  for  a  minute  or  so  in  order  to  administer  some  more  chloroform,  and 
throughout  the  remainder  of  the  operation  similar  pauses  will  occasionally  be 
necessary.  The  circle  of  mucosa  is  then  quickly  dissected  from  the  underlying 
tissue  up  to  the  duct,  after  which  a  stab  is  made  by  a  fine  scalpel  through  the  skin 
of  the  cheek  opposite  the  opening  of  the  duct,  the  edge  of  the  skin  incision  being 
trimmed  by  a  scissors  so  as  to  make  the  wound  elliptical  in  shape.  By  means  of 
a  surgical  needle  a  fine  silk  ligature  is  passed  through  the  anterior  edge  of  the 
circle  of  mucosa  and  its  free  ends  pulled  out  through  the  skin  wound.  By  gentle 

231 


232 


EXPERIMENTAL  PHYSIOLOGY. 


traction  on  the  ligature  and  by  bending  the  free  end  of  the  probe  out  through  the 
wound  the  duct  and  encircling  mucosa  is  brought  out  to  the  skin,  care  being  taken 
not  to  stretch  or  twist  the  duct.  The  edges  of  the  mucous  circle  are  now  stitched 
by  a  fine  silk  or  chromacised  catgut  ligature  to  the  edges  of  the  skin  wound.  The 
wound  in  the  mouth  is  similarly  stitched  and  without  the  application  of  any 
dressing  the  animal  is  allowed  to  come  out  of  the  anaesthetic.  The  wound  should 
be  bathed  daily  with  physiological  saline  and  a  free  secretion  of  saliva  occasionally 
stimulated  by  giving  the  animal  some  dry  food  (bread  crumbs). 

When  the  wound  has  healed,  it  will  be  necessary  to  accustom  the  dog  to  being 
strapped  into  a  suitable  holder  and  it  is  most  important  for  the  success  of  the 


FIG.  67.     Funnel  applied  to  skin  of  animal  for  collection  of  fistula  juices.     (Pavlov). 

observations  that  the  animal  should  be  trained  to  submit  to  the  harnessing 
without  fear  or  excitement.  The  knowledge  that  feeding  is  to  follow  soon  makes 
the  animals  eager  to  participate  in  the  proceedings.  To  collect  the  secretion 
Pavlov  uses  a  funnel,  made  out  of  wax  and  resin*  with  its  edges  flared  out  so  as  to 
form  a  flat  surface  to  apply  to  the  skin  (Fig.  67).  To  apply  the  funnel  the  hair 
around  the  duct  is  clipped  close  by  a  scissors  and  thoroughly  dried.  The  funnel 
is  then  moderately  warmed  and  the  flared  edge  firmly  pressed  on  the  cheek  to 
which  it  adheres,  after  which  the  narrow  end  is  attached  to  a  light  graduated  test- 
tube.  In  removing  the  funnel  care  must  be  taken  not  to  abrade  the  skin.  Holding 
a  warmed  metal  rod  near  the  edges  helps  to  loosen  the  attachment  to  the  skin 
*50  parts,  rosin ;  40  parts,  ferric  oxide  Fe2Os  and  25  parts  yellow  wax. 


SALIVARY  AND  GASTRIC  FISTULA. 


233 


Demonstration    10.  —  The 

during  the  following  conditions: 

1 .  When  various  foods  are 
fed  to  the  animal. 

2.  When  acid  solution  or 
dry  bread  crumbs  are  thrown 
into  the  mouth. 

3.  When    the    animal     is 
teased   with  a   bone    (which 
should  afterwards  be  given  to 
him). 

It  is  also  profitable  to 
train  the  animal  so  that  he 
learns  to  associate  a  certain 
sound  or  visual  impression 
with  the  subsequent  stimula- 
tion of  salivary  secretion,  as 
by  giving  him  bread  crumbs. 
The  experiments  on  con- 
ditioned reflexes  are  however 
more  striking  when  the  fistula 
is  one  involving  the  sub- 
maxillary  or  sublingual  ducts. 
The  exact  nature  of  the 
demonstrations  and  experi- 
ments on  material  of  this 
type  must  naturally  vary  with 
circumstances.  Advanced 
students  may  profitably  de- 
vote considerable  time  to  this 
work. 

The  Normal  Secretion 
of  Gastric  Juice. — Satis- 
factory demonstration  of  the 
secretory  activities  of  the 
gastric  glands  requires  the 
establishment  of  both  gastric 
and  cesophageal  fistulae  on  the  same  animal. 


secretion    should    be    observed 


Stomach  cannula.     See  context  for 


This  can  be  under- 


234 


EXPERIMENTAL  PHYSIOLOGY. 


taken  only  when  there  is  someone  who  can  devote  considerable 
time  every  day  to  the  proper  care  and  attention  of  the  animal.  A 
few  observations  may,  however,  be  made  on  an  animal  with  a 
gastric  fistula  alone. 

Method  for  Making  the  Gastric  Fistula. 

Through  an  incision  6-7  c.m.  long  in  the  linea  alba  just  below  the  sternum  the 
stomach  wall  is  caught  by  a  forceps  and  after  pulling  it  somewhat  over  to  the 


FIG.  69.     Stand  for  holding  animal  on  which  fistula  operation  has  been  per- 
formed.    (From  Tigerstedt's  "  Practical  Physiology".) 


right,  the  serous  coat  is  attached  to  the  edge  of  the  skin  wound  by  a  few  discon- 
tinuous sutures.  An  incision  is  then  made  through  all  the  coats  of  the  stomach 
wall,  bleeding  being  carefully  controlled  by  ligatures.  The  incision  is  just  large 
enough  to  admit  the  notched  flange  of  the  gastric  cannula  (Fig.  68).  A  cromi- 
cised  catgut  ligature  is  now  stitched  like  a  purse  string  a  short  distance  from  the 
edges  of  the  incision  and  the  cannula  inserted  and  tied  (not  too  tightly)  in  place 
by  the  ligature.  It  is  well  to  apply  a  second  purse  string  ligature.  The  operation 
i  s  completed  by  closing  the  skin  wound  up  to  the  cannula  with  discontinuous  sutures. 


SALIVARY  AND  GASTNIC  FISTULA.  235 

The  wound  is  then  dressed  with  cotton  and  collodion  and  the  outer  shield  of  the 
cannula  screwed  on,  but  not  so  far  as  to  press  on  the  wound.  The  tube  of  the 
cannula  is  closed  by  the  screw-in  stopper. 

Demonstration  11.— In  about  a  week,  when  the  wound  will 
usually  have  healed,  the  dog  is  placed  on  the  observation  holder  (Fig. 
69)  and  the  following  observations  are  made.  A  pledget  of  absorbent 
cotton  attached  to  a  hsemostat  is  passed  into  the  stomach  and 
gently  moved  over  the  mucosa;  the  nature  and  reaction  of  the 
secretion  which  adheres  to  it  after  removal  is  observed.  A  thin- 
walled  rubber  bag  attached  to  a  glass  tube  is  carefully  passed  into 
the  stomach  through  the  fistula  and  filled  with  warm  water.  The 
tube,  leading  out  of  the  fistula,  is  connected  with  a  water  mano- 
meter, the  free  limb  of  which  is  attached  by  tubing  to  a  sensitive 
tambour  arranged  to  inscribe  its  movements  on  a  drum.  Observa- 
tions are  now  made  on  the  hunger  contractions.  (It  may  be 
necessary  to  wait  some  time  before  these  appear).  When  satis- 
factory records  have  been  secured  the  animal  is  teased  by  tempting 
it  with  appetising  food  and  the  effect  on  the  contractions  noted. 

The  rubber  bag  is  now  removed  and  the  reaction  of  the  secretion 
adhering  to  it  tested  by  means  of  litmus  paper. 

These  observations  on  hunger  contractions  in  a  dog  should  be 
supplemented  by  similar  ones  on  man.  For  this  purpose  a  thin 
rubber  bag  is  firmly  tied  on  a  narrow  stomach  tube  and  passed 
down  the  oesophagus  until  the  bag  lies  in  the  stomach.  The  bag  is 
then  distended  by  air  (cf .  Carlson)  and  the  outer  end  connected  with 
a  water  manometer  and  tambour.  The  observation  should  be  made 
on  a  person  who  has  not  taken  food  for  some  hours  previously. 


CHAPTER   XXXIV. 

THE  MOVEMENTS  OP  THE  OESOPHAGUS*  AND 
INTESTINE. 

Demonstration  12. — A  rabbit  is  narcotised  by  means  of 
urethane  (p.  79) t  and  the  oesophagus  is  exposed.  This  is  accom- 
plished partly  by  drawing  the  trachea  to  the  right  by  a  stout  silk 
ligature  passed  around  it  and  partly  by  pulling  the  oesophagus 
to  the  left.  The  vagus  nerve  is  then  followed  up  to  where  the 
superior  laryngeal  leaves  it,  and  this  branch  is  cut  after  tying  a 
thread  round  it  as  near  to  the  vagus  as  possible.  Stimulation  of  the 
laryngeal  nerve  by  a  Faradic  current  excites  the  act  of  swallowing 
and  it  can  be  seen  that  this  consists,  in  order,  of  a  movement  of  the 
floor  of  the  mouth,  of  elevation  of  the  larynx  and  of  the  passage  of  a 
peristaltic  wave  along  the  cesophagus.  A  record  of  the  peristaltic 
wave  can  be  obtained  by  inserting  into  the  lumen  of  the  cesophagus, 
through  a  small  incision,  a  thin-walled  rubber  bag  (finger  cot),  which 
is  connected  by  tubing  with  a  water  manometer  and  tambour,  after 
distending  it  with  warm  water.  J 

It  is  now  important  to  ascertain  whether  the  peristaltic  wave 
can  be  more  readily  set  up  by  mechanical  irritation  of  the  ceso- 
phagus or  of  the  pharynx.  The  stimulation  can  be  produced  by 
stroking  with  a  feather.  The  cesophagus  is  finally  cut  across  and  a 
bent  pin  connected  by  a  thread  with  a  muscle  lever  attached  to  the 
peripheral  end  of  the  cut  tube.  The  superior  laryngeal  nerve  is 
again  stimulated.  From  the  results  of  this  observation  what  con- 
clusions can  be  drawn  concerning  the  manner  of  transmission  of  the 
oesophageal  peristaltic  wave? 

*The  action  of  the  base  of  the  tongue,  etc.,  in  swallowing  may  be  readily 
studied  in  the  decerebrate  cat,  as  described  on  p.  249. 

fFor  the  success  of  the  observation  the  anaesthesia  must  not  be  too  deep. 

Jit  is  best  to  tie  the  finger  cot  to  a  rubber  catheter  so  that  the  end  of  the  cath- 
eter reaches  to  the  end  of  the  cot.  This  facilitates  insertion  of  the  cot  into  the 
cesophagus.  It  is  important  to  see  that  the  cot  becomes  uniformly  distended  with 
water  before  connecting  with  the  water  manometer.  The  edges  of  the  incision 
in  the  cesophagus  should  be  stitched  together  so  as  to  hold  the  instrument  in  place. 

236 


MOVEMENTS  OF  OESOPHAGUS  AND  INTESTINE. 
THE  MOVEMENTS  OF  THE  INTESTINE. 


237 


Demonstration  13. — The  same  animal  may  now  be  used  for 
observations  on  the  intestinal  movements.  For  this  purpose  a 
tracheal  cannula  is  inserted  and  artificial  respiration  established.* 
The  thorax  is  then  opened  and  the  vagus  and  splanchnic  nerves 
quickly  cut,  this  procedure  being  necessary  in  order  to  secure  pro- 


FIG.  70.  Sherrington  Electrodes.  The  nerve  is  pulled  through  the  tube  by  means  of  a 
thread  attached  to  it,  and  is  arranged  so  that  it  lies  between  the  platinum  electrodes  inserted 
through  the  side  tube.  The  nerve  musto  n  no  i  ccount  be  stretched  when  being  pulled  into  the 
electrode 

nounced  intestinal  movements.  One  of  the  splanchnic  nerves  is 
connected  with  Sherrington's  electrodes  (Fig.  70)  the  wires  of  which 
emerge  from  the  wound.  The  thoracic  wound  is  closed  by  sutures, 
and  the  abdomen  opened  along  the  linea  alba.  The  animal  is  then 

*It  is  advisable  also  to  place  a  cannula  filled  with  saline  in  the  central  end 
of  the  jugular  vein.     Through  this  cannula  drugs  can  subsequently  be  injected. 


238  EXPERIMENTAL  PHYSIOLOGY. 

placed  in  a  bath  of  physiological  saline  at  about  33-35°  C,  contained 
in  a  tank  of  suitable  size  and  the  intestines  allowed  to  float  out  in 
the  saline.  The  pendular  movements  are  very  conspicuous  and 
the  loops  should  be  closely  examined  with  the  object  of  ascertaining 
which  of  the  muscular  coats  are  contracting.  If  no  peristaltic 
waves  are  observed,  they  may  be  set  up  by  pinching  the  intestine. 
Observe  closely  the  characteristics  of  these  waves. 

The  effect  produced  on  the  movements  by  stimulation  of  the 
peripheral  end  of  the  splanchnic  nerve  is  now  studied. 

Records  of  the  movements  may  be  secured  by  the  balloon 
method  already  described  for  the  oesophagus. 

Finally,  if  the  animal  is  still  in  suitable  condition,  the  effect 
produced  on  the  intestinal  movements  by  injections  into  the  jugular 
vein  of  epinephrin  (1-10,000  adrenalin  chloride)  and  of  atropine 
are  observed. 


SECTION  VIII. 
THE  CENTRAL  NERVOUS  SYSTEM. 

CHAPTER    XXXV. 

REFLEX  ACTION  IN  THE  MAMMALIA. 

Although  certain  basic  facts  concerning  the  physiology  of  reflex 
action  can  be  learned  by  observations  on  the  spinal  frog  (p.  90)  the 
variety  and  complexity  of  the  reflex  movements  exhibited  by  the 
preparation  are  too  limited  to  enable  us  to  understand  much  about 
reflex  action  in  the  higher  animals.  Practically  the  only  reflex 
movement  elicitable  in  the  spinal  frog  is  the  flexion  reflex,  which  is 
of  a  type  quite  different  from  that  of  the  reflexes  that  are  concerned 
in  maintaining  such  animals  as  the  dog  or  man  in  the  erect  posture 
(postural  reflexes),  or  in  enabling  movement  to  occur  from  place  to 
place.  The  functional  unit  of  the  nervous  system  is  the  reflex  arc 
and  the  ability  to  perform  complex  co-ordinated  movements  de- 
pends on  the  integration  of  the  various  reflex  arcs  among  one  another 
—the  integrative  action  of  the  nervous  system  (Sherrington).  In 
order  that  we  may  study  the  principles  that  govern  this  integration 
it  is  necessary  to  simplify  the  conditions  from  those  obtaining  in 
the  intact  animal,  which  is  done  by  breaking  the  connection  between 
the  higher  brain  centres  and  those  of  the  lower  portion  of  the  spinal 
cord  (the  spinal  animal). 

Demonstration  14. — The  most  satisfactory  preparation  to 
use  for  a  study  of  the  spinal  reflexes  is  one  in  which  the  spinal  cord 
has  been  cut  some  weeks  previous  to  the  observation.  Spinal  shock 
will  have  been  recovered  from  and  the  following  reflex  movements 
can  readily  be  demonstrated  :* 

*These  can  readily  be  demonstrated  with  the  animal  lying  on  his  side,  but  if 
graphic  records  are  desired,  as  for  measuring  latent  periods,  etc.,  it  is  best  to  sus- 
pend the  animal  in  a  suitable  stand  with  the  posterior  extremities  hanging  free. 
Threads  attached  near  the  paws  are  carried  over  directing  pulleys  (or  glass  rods) 

239 


240  EXPERIMENTAL  PHYSIOLOGY. 

1.  THE  FLEXION  REFLEX — 'by  pricking   the  skin  of  the   paw 
with  a  pin  or  applying  a  moderately  strong  electric  shock.     The 
flexion  at  knee  and  hip  is  accompanied  by  extension  of  the  leg  of  the 
opposite  side,  THE  CROSSED  EXTENSION  REFLEX.      By  taking  simul- 
taneous tracings  of  the  two  legs  after  attaching  the  feet  to  suitable 
levers  by  threads,  the  correspondence  in   time  between  the  two 
reflexes  is  demonstrated. 

2.  THE  KNEE  JERK — by  giving  a  sharp  blow  with  a  ruler  or 
the  handle  of  a  scalpel  to  the  ligamentum  patellae.     Note  that  the 
leg  swings  limply  back  to  its  flexed  position  after  the  tap  (compare 
with  the  behaviour  of  the  jerk  in  a  decerebrate  animal  (p.   103  ). 

3.  THE  SCRATCH  REFLEX — by  moving  the  finger  or  a  pencil 
backwards  and  forwards  on  the  skin  of  the  body.     The  skin  area 
from  which  the  reflex  can  be  elicited  is  very  extensive  and  the  paw 
usually   is   directed   approximately   to    the   place   of   stimulation 
('local  sign').     Sometimes  this  property  of  'local  sign',  however,  is 
very   imperfect.     An   electrical   stimulus    (through   the   stigmatic 
electrode)  will  also  elicit  the  reflex,  but  much  less  satisfactorily  than 
the  mechanical  one. 

4.  THE  EXTENSOR  THRUST — by  pushing  the  blunt  end  of  a 
pencil  between  the  pads  of  the  paws.     The  corresponding  leg  makes 
a  sudden  extension  movement. 

The  following  properties  of  reflex  action  may  now  be  studied 
using  one  or  other  of  the  foregoing  reflexes. 

1.  THE  LATENT  PERIOD  OR  UNCORRECTED  REFLEX  TIME.  To 
determine  this  it  is  necessary  to  employ  electrical  stimulation  and  to 
insert  a  signal  magnet  in  the  primary  circuit.  A  fast  rate  of  drum 


to  be  attached  to  the  long  arm  of  a  right  angled  lever,  from  the  short  arm  of  which 
a  second  thread  runs  to  a  straight  muscle  lever.  The  threads  are  adjusted  so  as 
suitably  to  diminish  the  amplitude  of  movement  at  the  writing  points. 

A  large  electrode  made  out  of  a  strip  of  copper  covered  with  a  pad  of  surgica 
gauze,  which  is  moistened  with  salt  solution,  is  tied  on  to  the  middle  of  the  back 
(indifferent  electrode)  and  a  much  smaller  electrode  of  the  same  type  is  tied  to  the 
foot  of  one  side  (stimulating  electrode).  A  third  (stigmatic)  electrode  composed 
of  a  stout  copper  wire  covered  at  its  tip  by  a  piece  of  surgical  gauze  is  also  required 
The  wires  leading  from  the  electrodes  are  connected  with  the  secondary  coil  of  an 
inductorium,  the  indifferent  electrode  with  one  pole  and  the  stimulating  and 
stigmatic  electrodes  with  the  other.  (A  well  insulated  simple  key  should  be 
inserted  in  the  wire  leading  from  the  attached  foot  electrode). 


REFLEX  MOVEMENTS  IN  MAMMALS.  '  241 

must  be  used,  the  exact  relationship  of  the  signal  pointer  to  the 
recording  lever  being  indicated  by  alignment  marks  (see  p.  94). 
A  time  tracing,  preferably  of  1/100  sec.  must  also  be  taken.  Several 
observations  on  the  flexion  reflex  with  stimuli  of  varying  strength 
will  show  the  latent  period  to  vary  from  about  0.03  to  0.12  sec. 
The  latent  time  of  the  jerk  is  much  shorter.  (The  signal  for  the 
application  of  the  stimulus  is  afforded  in  this  case  by  the  slight 
movement  of  the  lever  produced  by  the  blow  to  the  tendon,  the 
attachment  of  the  threads  to  the  levers  being  adjusted  so  as  to  make 
them  sensitive  enough  to  record  this). 

The  latent  period  of  the  scratch  reflex  (using  the  stigmatic 
electrode)  is  relatively  very  long  and  it  varies  with  the  strength  of 
the  stimulus.  Taking  these  results  with  those  already  attained 
on  the  palpebral  reflex  (p.  104)  into  consideration,  what  con- 
clusions do  you  draw  concerning  the  latency  of  reflex  action  in 
general?  What  corrections  must  be  made  to  determine  the  true 
or  reduced  reflex  time? 

2.  GRADING  OF  INTENSITY. — This  is  investigated  for  the  flexion 
and  scratch  reflexes  by  varying  the  strength  of  the  electrical  stimu- 
lus and  for  the  extensor  thrust  by  applying  varying  degrees  of 
pressure  to  the  paws.     How  do  the  results  obtained  from  these  two 
types  of  reflex  compare  with  those  already  obtained  for  the  palpe- 
bral reflex? 

3.  SUMMATION.     Using  the  flexion  reflex,  a  strength  of  current 
is  found  which  is  just  ineffectual  when  single  shocks  are  applied, 
a  simple  tapping  key  being  inserted  in  the  primary  circuit  of  the 
inductorium  in  place  of  the  vibrating  hammer.    The  shocks  are  then 
applied  frequently.     Is  the  summation  more  pronounced  than  you 
found  it  to  be  for  isolated  nerve  ? 

4.  AFTER  EFFECT. — By  recording  the  movement  of  the  flexion 
reflex  on  a  fairly  rapid  drum,  the  degree  of  after  effect  in  relation- 
ship to  the  strength  of  stimulus  is  observed.        Both  single  shocks 
and  tetanizing  shocks  are  employed.       hi  what  respects  do  the 
results  differ  from  those  obtained  on  a  nerve? 

5.  REFLEX  FATIGUE. — The  effect  of  maintained  stimulation  is 
studied  in  the  flexion  and  scratch  reflexes,  using  a  slow  drum.     How 
does  reflex  fatigue  differ  from  fatigue  in  an  isolated  nerve-muscle 
preparation?      After  the  leg  has  been  thoroughly  fatigued  for  the 


242  EXPERIMENTAL  PHYSIOLOGY. 

flexion  reflex,  the  scratch  reflex  is  elicitated  by  mechanical  and 
electrical  stimuli.  What  do  the  results  indicate  as  to  the  locus  of 
fatigue  in  the  reflex  arc? 

6.  IMMEDIATE  INDUCTION. — The  end  of  the  handle  of  a  scalpel 
or  of  a  small  ruler  is  pressed  against  the  skin  of  a  scratch  area,  but 
there  is  no  response.     If  the  same  object  be  moved  on  the  skin, 
however,  the  scratch  movement  is  likely  to  be  set  up.     What  is  the 
explanation  of  the  result?     What  is  the  analagous  experiment  on 
vision? 

7.  SUCCESSIVE  INDUCTION. — Using  a  slow  drum,  record  a  con- 
siderable number  of  knee  jerks  produced  by  regularly  applied  taps 
of  as  nearly  as  possible  equal  intensity  to  the  patellar  tendon,  and 
when  there  is  approximate  equality  in  the  heights  of  the  contrac- 
tions throw  the  corresponding  leg  for  a  few  seconds  into  the  flexion 
reflex,  meanwhile  continuing  the  patellar  taps.     When  the  flexion 
reflex  subsides  the  tendon  jerks  are  greatly  exaggerated.     Explain 
why    this   shows    successive   induction.     Demonstrate    the   same 
phenomenon  for  the  flexion  reflex  and  extensor  thrust,  and  for  the 
crossed  extension  reflex  and  flexion  reflex.     What  is  the  analagous 
experiment  on  vision? 


CHAPTER   XXXVI. 

CEREBRAL  LOCALIZATION,   DECEREBRATE  RIGIDITY, 

RECIPROCAL  INNERVATION,  FUNCTIONS  OF 

SPINAL   ROOTS  IN  THE  MAMMAL  (DOG.) 

Demonstration  15. 

A  tracheal  cannula  is  inserted  in  an  etherized  dog,  and  ligatures  placed  loosely 
around  the  carotid  arteries  on  both  sides.  With  the  animal  in  the  prone  position 
the  head  is  raised  by  placing  a  pad  under  it,  being  careful  to  see  that  there  is  no 
kinking  of  the  tube  leading  from  the  tracheal  cannula  to  the  ether  bottle.  To 
serve  as  a  landmark  for  the  crucial  sulcus  of  the  cerebrum  (which  corresponds  to 
the  Rolandic  fissure  on  the  human  brain)  two  threads  are  stretched  across  the 
head,  one  of  them  joining  the  outer  canthi  of  the  eyes  and  the  other,  the  condyles 
of  the  lower  jaw.  The  crucial  sulcus  lies  a  little  behind  the  mid-point  between 
the  two  threads.  An  incision  is  made  along  the  mid-line  of  the  scalp  and  by  blunt 
dissection  the  temporal  muscle  is  separated  from  the  bone  far  enough  to  make 
room  for  two  trephine  holes  one  in  front  of  the  other  and  with  their  inner  margins 
at  least  3  mm.  from  the  mid  line  so  as  to  avoid  wounding  the  superior  longitudinal 
sinus.  To  manipulate  the  trephine,  the  steel  point  is  first  of  all  adjusted  so  that 
it  projects  beyond  the  sawing  edge,  and  this  point  is  bored  into  the  skull  in  order 
to  afford  good  fixation.  When  the  sawing  edge  reaches  the  bone,  care  is  taken  it 
cuts  uniformly,  and  when  a  good  start  has  been  made  the  central  point  is  pulled 
up  so  that  this  may  not  puncture  the  brain  The  trephining  is  continued  until 
the  inner  table  of  the  skull  is  cut  through  around  most  of  the  circle,  the  trephine 
is  then  removed,  and  the  disc  of  bone  pried  up  by  means  of  a  pereosteal  elevator 
or  a  stout  pair  of  forceps.  There  is  apt  to  be  considerable  haemorrhage  at  this 
stage,  but  it  can  usually  be  controlled  by  applying  for  a  few  minutes  a  pad  of 
gauze  thoroughly  wrung  out  with  hot  isotonic  saline.  When  the  two  trephine 
holes  have  been  made  they  are  connected  together  by  bone  forceps,  taking  care 
not  to  wound  the  brain  and  controlling  bleeding  with  hot  gauze.  A  curved  sur- 
gical needle  is  passed  through  the  dura  and  by  means  of  it  the  latter  is  raised 
sufficiently  so  as  to  be  able  to  cut  it  with  a  sharp  pointed  scissors.  The  exposed 
brain  should  be  covered  with  gauze  soaked  in  isotonic  saline. 

In  order  to  stimulate  the  cortex  a  large  plate  (indifferent) 
electrode  is  placed  on  the  moistened  skin  of  the  lower  dorsal  region 
and  connected  with  one  terminal  of  the  secondary  coil  of  an  in- 
ductorium  with  the  other  terminal  of  which  a  blunt-pointed 
(stigmatic  or  diagnostic)  electrode  is  connected. 

Having  made  a  rough  sketch  indicating  the  position  of  sulci  and 

243 


244 


EXPERIMENTAL  PHYSIOLOGY. 


convolutions  of  the  exposed  portion  of  the  cerebrum,  the  front  and 
hind  legs  on  the  side  opposite  to  the  opening  in  the  skull  are  loosen- 
ed and  the  tetanizing  current  applied  for  short  periods  and  at  vary- 
ing strengths  until  definite  movements  are  observed  to  occur.  For 
successful  results  it  is  necessary  to  have  the  animal  as  lightly 
anaesthetized  as  is  consistent  with  the  entire  absence  of  pain. 


N  . 


n.  -.. 


FIG.  71.  Surface  of  cerebrum  of  dog,  showing  on  the  left  side  approximate 
positions  of  the  various  centres:  n,  neck;  fl.,  forelimb;  hi,  hindlimb;  f,  face.  Move- 
ments of  the  eyes,  E,  accompanied  by  dilation  of  the  pupil,  P,  are  also  obtained  from 
the  portions  of  the  cortex  indicated  on  the  right  side.  (After  Stewart) . 

When  a  suitable  strength  of  stimulation  has  been  found,  the  exposed 
area  of  cerebrum  is' systematically  explored  (Fig.  71),  and  the  ob- 
served responses  noted  on  the  sketch.  The  character  of  the  move- 
ments must  also  be  carefully  noted  (i.e.,  whether  there  is  evidence 
of  reciprocal  innervation,  etc.).  The  pupils  and  eye  movements  on 
both  sides,  movements  of  the  head  and  ears,  changes  in  the  respira- 
tions and  movements  of  the  tail  must  also  be  looked  for.  The 


CEREBRAL  LOCALIZATION.  245 

general  results  are  indicated  in  the  accompanying  chart.  Finally 
the  effect  of  the  application  for  some  time  of  a  very  strong  stimulus 
is  studied. 

The  animal  is  finally  decerebrated.  For  this  purpose  a  large 
aneurysm  needle  is  passed  through  the  posterior  edge  of  the  trephine 
hole  backwards  until  the  tentorium  cerebelli  is  felt.  It  is  then 
directed  downwards  and  inwards  so  as  to  break  across  the  base 
of  the  brain  stem  just  in  front  of  the  tentorium.  Immediately  this 
is  done  the  respirations  are  likely  to  cease  or  to  become  very  irregular 
so  that  artificial  respiration  must  be  started.  The  ether  can  now 
be  discontinued  since  the  animal  is  incapable  of  feeling  any  pain. 
The  muscles  of  the  extremities  are  carefully  observed  from  time 
to  time  for  the  onset  of  decerebrate  rigidity  and  for  the  appearance 
of  reflex  movements,  such  as  the  knee  jerk  and  the  flexion  reflex. 

For  the  purpose  of  studying  recriprocal  innervation*  the 
tendons  of  the  rectus  femoris  and  the  semitendinosus  are  exposed 
and  isolated  from  adherent  aponeurosis  on  both  sides  and  the 
tendons  are  cut  after  threads  have  been  tied  to  them.  The  peroneal 
nerves  are  also  exposed  as  they  lie  under  the  skin  on  the  inner  side 
of  the  leg  or  the  dorsum  of  the  foot.  After  attaching  threads  and 
cutting,  each  nerve  is  placed  in  a  pair  of  Sherrington's  electrodes 
attached  to  an  inductorium.  The  threads  on  the  tendons  are  con- 
nected with  muscle  levers,  by  means  of  pulleys  or  angle  levers, 
and  the  writing  points  are  arranged  so  that  they  write  in 
the  same  perpendicular  on  the  drum,  signal  magnets  being 
inserted  in  the  primary  circuits  of  the  two  inductoria.  When  the 
peroneal  nerve  on  one  side  is  stimulated  it  will  be  found  that  the 
homolateral  semitendinosus  contracts,'  and  that  the  rectus  femoris 
simultaneously  relaxes,  if  it  be  in  a  hypertonic  condition  (as  a  result 
of  decerebrate  rigidity).* 

If  the  preparation  is  still  in  suitable  condition,  the  experiment 
should  be  terminated  by  exposing  the  lumbar  portion  of  the  spinal 
cord  and  studying  THE  FUNCTIONS  OF  THE  SPINAL  ROOTS,  noting  also 
the  effect  produced  on  the  rigidity  by  their  section.  To  expose  the 
roots,  place  the  animal  on  its  belly  with  a  thick  pad  or  block  of  wood 
under  the  lower  portion  of  the  abdomen,  and  make  an  incision  in 
the  mid  line  of  the  back  over  the  spines  of  the  lumbar  vertebrae. 
Separate  the  muscles  from  both  sides  of  the  spinous  processes  and 

*This  experiment  succeeds  best  on  the  decerebrate  cat.     If  time  is  limited 
the  experiment  should  be  omitted  and  that  on  the  spinal  roots  performed. 


246  EXPERIMENTAL  PHYSIOLOGY. 

retract  strongly  so  that  the  laminae  of  the  vertebrae  are  exposed. 
Much  of  this  can  be  done  by  blunt  dissection,  which  will  avoid 
haemorrhage.  Cut  the  tissues  between  the  spinous  processes  of  the 
2nd  and  3rd  lumbar  and  also  between  the  last  lumbar  and  1st 
sacral  and  amputate  at  their  bases,  the  spinous  processes  between 
the  two  cuts,  using  a  strong  bone  forceps.  Remove  the  spinous 
processes  and  after  bleeding  has  been  controlled  by  the  application 
of  cloths  wrung  out  with  hot  water  proceed  to  open  the  spinal  canal 
by  cutting  through  the  laminae  of  the  exposed  vertebrae  with  bone 
forceps,  taking  care  that  the  point  of  this  instrument  does  not  go 
deeply  into  the  spinal  canal.  The  spinal  cord  enclosed  in  the  dura 
is  now  exposed,  but  it  is  necessary  in  order  to  expose  the  roots 
properly  that  the  articular  processes  between  neighbouring  verte- 
brae be  picked  away.*  (The  so-called  hawk's  bill  bone  forceps  are 
useful  for  this  process). 

The  posterior  root  ganglia  came  into  view  when  the  articular 
processes  have  been  removed.  After  again  stopping  haemorrhage, 
which  is  likely  to  be  considerable  at  this  stage,  the  roots  are  pre- 
pared for  stimulation. 

Lift  the  posterior  root  of  the  6th  nerve  carefully  on  a  strabismus 
hook  or  small  aneurysm  needle,  and  tie  a  ligature  round  it  as  near 
to  the  ganglion  as  possible,  cutting  the  root  distal  to  the  ligature. 
Loosen  the  leg  on  the  corresponding  side  and  stimulate  the  central 
end  of  the  root  with  a  tetanising  current,  using  ordinary  electrodes. 
Note  the  character  of  the  movements  of  the  leg  and  watch  for  any 
changes  in  the  respirations. 

Ligate  and  cut  the  7th  posterior  root  as  near  the  cord  as  possi- 
ble and  stimulate  the  peripheral  end. 

What  conclusion  do  you  draw  from  the  results  of  these  experi- 
ments? 

The  functions  of  the  anterior  roots  are  then  determined  by  a 
repetition  of  the  same  procedure  as  for  the  posterior.  It  is  some- 
what difficult  to  prepare  these  roots  for  stimulation,  and  it  often 
assists  to  pass  a  tape  round  the  cord,  by  which  it  is  cautiously  pulled 
up  and  to  one  side.  Observe  carefully  any  difference  in  the  type 
of  movement  which  results  by  stimulating  the  anterior  and  posterior 
roots. 

Draw  a  diagram  showing  the  functions  of  the  roots. 

*It  will  be  observed  that  the  lower  (6th  and  7th)  lumbar  roots  are  larger  than 
those  higher  up,  the  level  of  the  7th  being  about  on  a  line  with  the  iliac  crests. 


CHAPTER    XXXVII. 


THE  DECEREBRATE  CAT  I. 

Demonstration  16. 

A  cannula  is  inserted  in  the  trachea  in  a  deeply  etherized  cat  (preferably  a  young 
animal)  and  a  pair  of  serres  fines  is  placed  on  the  carotid  arteries  on  both  sides  of 
the  neck.  The  animal  is  then  placed  on  the  '  decerebrator '  with  the 
pelvis  resting  on  the  back  platform  (P),  the  hind  legs  hanging  free,  and  the 
neck  on  the  neck  block  (N),  care  being  taken  to  prevent  any  kinking  of  the 


FIG.  72.     Decerebrator.     For  description,  see  context. 

tracheal  cannula.  The  nasal  septum  is  punctured  by  a  scaplel  and  a  cord  is  pass- 
ed through  to  a  hole  on  the  neck  block,  at  the  lower  level  of  the  tongue  guard  (T). 
The  mouth  is  opened  and  by  gentle  traction  on  the  cord  and  manipulation  of  the 
head  the  snout  is  pulled  over  the  tongue  guard  which  lies  over  the  tongue  with  its 
point  between  the  fauces  and  over  the  epiglottis.  The  cord  is  then  tied  to  a  hook 
on  the  base  of  the  stand  and  the  nose  piece  (S)  is  pressed  up  against  the  snout 
and  fixed  in  position  by  tightening  the  clamp. 

An  incision  is  now  made  along  the  mid  line  of  the  skull  and  the  skin  reflected 
to  both  sides.     A  distance  of  30  mm.  is  measured  back  from  the  coronal  suture 

247 


248  EXPERIMENTAL  PHYSIOLOGY. 

(which  is  particularly  evident  in  young  animals)  and  marked  by  a  cut  with  a 
scalpel.  The  preparation  is  now  ready  for  decerebration.  This  is  best  done  by 
using  a  planing  blade  (12.5  cm.  wide,  9  cm.  high  and  4  cm.  thick)  bevelled  on  one 
edge  and  mounted  on  a  wooden  handle,  but  a  good  ax  of  about  the  same  dimen- 
sions is  quite  satisfactory.  To  perform  the  decerebration,  the  operator  holding 
the  blade  in  the  left  hand,  places  the  edge  on  the  notched  mark,  and  holds  the 
plane  of  the  blade  at  right  angles  to  the  plane  of  the  head.  By  means  of  a  heavy 
mallet  (or  hammer,  if  an  ax  is  used)  held  in  the  right  hand  he  gives  the  blade  a 
light  blow  so  as  to  make  the  edge  engage  the  skull,  the  blade  being  held  accurately 
transverse  to  the  long  axis  of  the  skull  and  directed  so  that  when  the  head  is  cut 
through  the  edge  will  strike  a  mark  made  on  the  metal  plate  of  the  base  of  the 
tongue  guard.  The  operation  is  then  completed  by  applying  a  couple  of  strong 
blows  and  the  decerebrated  animal  is  immediately  removed  from  the  stand  and 
placed  on  its  back  on  the  table,  the  neck  being  grasped  with  the  finger  and  thumb 
just  below  the  transverse  process  of  the  atlas  so  as  to  compress  the  vertebral 
arteries.  The  head  is  kept  elevated  to  diminish  haemorrhage,  and  etherization  is 
discontinued.  In  many  animals  the  respirations  cease  for  a  few  moments,  and 
artificial  respiration  may  be  necessary.  They  usually  return  spontaneously,  but 
if  they  do  not  do  so,  the  vertebral  arteries  should  be  momentarily  released  so  as  to 
allow  some  blood  to  flow  to  the  respiratory  centre.  The  bleeding  from  the  cut 
across  the  head  is  not  usually  serious  if  the  vertebrals  are  properly  compressed 
and  when  time  has  been  allowed  for  clotting  to  occur  these  may  be  cautiously 
released.  There  is  no  particular  advantage  in  trying  to  accelerate  the  clotting 
by  applying  absorbent  cotton  wool  to  the  wound.  It  usually  takes  from  15  to  20 
minutes  before  the  vertebrals  can  be  entirely  released.  Finally,  the  clamps  are 
removed  from  the  carotid  arteries,  one  at  a  time — any  bleeding  point  in  the  cut 
muscles  being  ligated — and  the  head  is  tied  to  an  upright  so  as  to  keep  it  elevated. 

The  resulting  preparation  is  suitable  for  many  experimental 
purposes  (consult  Sherrington's  Mammalian  Physiology,  The 
Clarendon  Press,  Oxford.) 

The  blood  pressure,  although  it  may  rise  considerably  while 
the  vertebrals  are  being  compressed  (because  of  partial  asphyxia) 
soon  returns  to  about  the  normal  level,  and  the  respiratory  centre 
responds  to  changes  in  CH  of  the  blood  much  more  promptly  than 
in  anaesthetised  animals.  Why  should  this  be  the  case?  It  is 
particularly  in  the  study  of  reflex  actions,  however,  that  the  pre- 
paration is  of  value,  although  certain  of  them  are  masked  by  the 
decerebrate  rigidity  which  develops.  Since  the  section  if  properly 
made  goes  through  the  mesencephalon  just  behind  the  anterior 
corpora  quadrigemina,  reflexes  involving  the  head  end  of  the  animal 
can  be  demonstrated.  The  following  are  to  be  elicited  and  studied : 
1.  THE  PINNA  REFLEX. — Pinch  or  slightly  twist  the  tip  of  the 

pinna  between  the  finger  and  thumb.     The  response  consists  of 


THE  DECEREBRATE  PREPARATION.  249 

a  quick  retraction  of  the  pinna  accompanied  often  by  a  folding 
back  of  its  free  end. 

2.  THE  ACOUSTIC  REFLEX. — Pricking  up  of  the  ears  when  a  sharp 
sound  is  made  as  by  clapping  the  hands.     This  reflex  occurs 
only  when  the  section  is  forward  of  the  anterior  corpora  quad- 
rigemina. 

3.  THE    DEGLUTITION    REFLEX. — Swallowing    movements   when 
water  is  dropped  on  the  base  of  the  tongue.     Note  the  behaviour 
of  the  respiratory  movements  during  the  swallows.     Repeat  the 
observation  by  dropping  the  water  on  various  parts  of  the  tongue. 
Observe  the  effect  on  swallowing  produced  by  pressing  a  moist- 
ened camel's  hair  brush  on  the  pharynx.     In  order  to  do  this, 
it  is  necessary  to  slit  the  soft  palate  in  the  mid  line.     The  move- 
ments of  the  vocal  cords  can  readily  be  observed  by  using  a 
laryngeal  mirror. 

4.  THE  HEAD-SHAKE    REFLEX. — Rapid    shaking    movements    in 
rotary  direction  when  air  is  blown  into  the  external  auditory 
meatus.     The  reflex  may  also  be  elicited  by  squirting  cold  water 
from  a  syringe  into  the  ear. 

5.  THE  FLEXION  REFLEX. — By  painful  stimulation  of  the  paw — 
flexion  at  knee  and  hip  occurs. 

6.  THE  KNEE  JERK. — Quick  extension  (kick)  at  knee  produced  by 
tapping  the  patellar  tendon.     Note  particularly  that  the  return 
of  the  leg  after  the  contraction  is  not  complete,  and  that  if  the 
tendon  be  tapped  at  short  intervals  the  knee  becomes  more  or 
less  permanently  extended.     This  result  depends  on  a  contrac- 
tion remainder,  which  is  a  feature  of  the  'rigid'  postural  muscles 
in  decerebrate  preparations.     In  the  spinal  animal  there  is  no 
postural  hypertonus  so  that,  the  leg  passively  falls  back  to  its 
previous  position  after  the  jerk. 

The  scratch  reflex  is  not  present  as  a  rule. 

The  most  striking  reflex  condition  produced  by  the  decere- 
bration  is  the  rigidity,  which  it  can  readily  be  seen  affects  parti- 
cularly the  extensor  (postural)  muscles.  The  rigidity  is  not  of  the 
same  nature  as  the  tetanic  contraction  produced  by  continuous 
stimulation  of  the  motor  neurone,  for  the  muscle  yields  to  a  slowly 
applied  pull  and  does  not  spring  back  to  its  old  position  when  the 
extending  force  is  removed.  This  is  tested  by  bending  the  knee  or 


250  EXPERIMENTAL  PHYSIOLOGY. 

elbow  joints.  The  condition  has  therefore  been  styled  '  REFLEX 
POSTURAL  TONUS  '  and  it  can  be  shown  that  the  weight  required  to 
counterbalance  the  rigid  muscle  is  practically  the  same  whether 
muscle  is  lengthened  (knee  in  extension)  or  shortened  (knee 
in  flexion).* 

If  the  preparation  is  still  in  suitable  condition,  the  experiment 
should  be  terminated  by  exposing  the  lumbar  portion  of  the  spinal 
cord  and  cutting  the  sensory  roots  of  the  nerves  of  the  hind  limbs 
What  effect  has  this  procedure  on  the  decerebrate  rigidity?  What 
conclusions  do  you  draw  from  the  results? 


*The  flexor  muscles  acting  on  the  joint  should  be  paralysed  by  cutting  their 
nerves  in  testing  these  points. 


CHAPTER    XXXVIII. 
THE  DECEREBRATE  CAT  II. 

THE  DECEREBRATE  PIGEON. 

There  are  certain  fundamental  reflex  reactions  which  can  be 
studied  only  after  considerable  operative  preparation  of  the  animal. 
One  of  these  is  RECIPROCAL  INHIBITION  which  the  following  experi- 
ment devised  by  Sherrington  clearly  demonstrates.  In  it  reflex 
inhibition  is  demonstrated  of  the  plastic  tonus  of  the  extensor 
muscles  of  the  knee  in  decerebrate  rigidity  and  of  the  same  muscles 
while  actively  contracted  as  a  result  of  reflex  stimulation. 

Demonstration  17. 

Whenever  bleeding  has  stopped  from  the  neck  stump  of  a  decerebrate  pre- 
paration (cat)  this  is  placed  on  its  back  on  a  well-heated  operating  table  and  the 
hind  limbs  tied  in  an  extended  position.  With  the  left  leg  well  abducted,  an 
incision  is  made  about  5  cm.  long  down  the  thigh  towards  the  outer  border,  and 
then  curved  across  the  thigh  towards  the  inner  border.  The  bluntly  V-shaped 
skin  flap  is  reflected  along  with  the  subcutaneous  fat  towards  the  median  line, 
so  as  to  expose  the  femoral  artery  and  vein.  About  8  cm.  outside  the  artery 
will  be  seen  the  psoas  muscle  with  the  femoral  nerve  emerging  from  it.  There  are 
three  branches  of  the  nerve.  Of  these  the  outermost  (a  small  branch)  runs  to  the 
sartorious  muscle  and  is  cut,  the  middle  (a  large  branch)  runs  to  the  quadriceps 
extensor  and  is  left  intact  and  the  innermost  (a  small  branch)  is  the  saphenous 
nerve,  which  also  is  cut.  Finally,  the  psoas  muscle  is  cautiously  cut  across  piece 
by  piece,  using  small  scissors  for  the  purpose.  By  these  operations  the  flexor 
muscles  of  the  hip  joint  are  rendered  incapable  of  acting  on  this  joint.  The 
operations  are  repeated  on  the  right  leg. 

The  sciatic  nerves  on  both  sides  must  now  be  exposed,  cut  low 
down  and  the  central  ends  placed  in  Sherrington's  electrodes,  the 
branches  of  them  that  run  to  the  hamstring  muscles  being  severed. 
By  this  latter  operation  the  knee  joint  is  rendered  incapable  of 
active  flexion.  To  accomplish  these  objects  an  incision  is  made 
down  the  mid  line  of  the  back  of  the  thigh,  starting  above  from  a 
point  midway  between  the  tuber  ischii  and  the  great  trochanter  and 
continuing  down  to  the  outer  condyle  of  the  femur.  From  the 

251 


252  EXPERIMENTAL  PHYSIOLOGY. 

upper  and  lower  ends  of  this  incision,  short  incisions  are  made  across 
the  limb  and  the  skin  flap  is  reflected  forward.  At  the  upper  end 
of  the  exposed  wound  the  lower  edge  of  the  relatively  small  gluteus 
maximus  muscle  is  made  out  (a  small  vein  running  along  its  lower 
border)  and  is  cut  at  its  lower  end  and  reflected  upward.  It  is  now 
possible  by  retracting  the  muscles  between  which  it  lies  to  separate 
the  sciatic  nerve  and  to  make  out  a  large  branch  passing  backwards 
from  it.  This  is  the  hamstring  nerve  and  it  is  cut.  The  sciatic 
nerve  is  next  followed  downwards  to  where  the  two  divisions  of  the 
trunk  (peroneal  and  tibial)  diverge.  A  ligature  is  tied  around  the 
nerve  at  this  point,  the  nerves  cut  distal  to  the  ligature  and  their 
central  ends  placed  in  Sherrington's  electrodes.  It  will  be  noted 
that  the  above  nerve  sections  render  practically  all  muscles  in  the 
thigh  incapable  of  reflex  contraction  except  the  extensor  muscles. 

It  is  now  necessary  to  arrange  for  graphic  records  of  movements 
at  the  knee  joint.  For  this  purpose  the  leg  is  amputated  near  the 
ankle  joint.  After  tying  a  stout  mass  ligature  (threaded  by  a  pack 
needle  through  the  skin  and  muscles  around  the  stump  so  as  to  hold 
it  in  place)  a  thread  is  also  attached  to  the  skin  of  the  stump,  and  con- 
nected with  a  suitable  muscle  lever,  using  pulleys  if  necessary. 
The  femur  must  also  be  immobilized  at  its  lower  end  so  that  the 
knee  joint  may  be  held  in  a  flexed  position  and  the  slightest  move- 
ment at  this  joint  recorded  without  disturbance  by  any  other  move- 
ments of  the  preparation.  For  this  purpose  it  is  necessary  to 
insert  a  threaded  steel  pin  into  the  condyles  of  the  femur  on  their 
median  aspect.  To  insert  the  drill  pin,  an  ordinary  drill,  procurable 
at  any  hardware  shop,  is  used.  The  drill  head  is  unscrewed  from 
the  pin  after  this  has  been  screwed  into  the  bones  and  a  brass  rod, 
threaded  at  one  end  so  that  it  fits  the  thread  of  the  screw  pin,  is 
connected  to  the  pin  with  its  outer  end  held  by  a  clamp  to  an  up- 
right stand. 

These  preliminary  operations  being  completed,  the  preparation 
is  placed  on  its  right  side,  and  the  femur  of  the  left  thigh  arranged 
so  that  it  is  supported  by  the  drill  pin  and  brass  rod  in  a  nearly 
vertical  position,  with  the  hips  flexed  almost  to  a  right  angle. 
In  cases  in  which  the  decerebrate  rigidity  is  marked,  the  left  knee 
will  be  nearly  extended.  If  it  is  not  so,  it  may  be  placed  in  this 
position  by  passive  extension  (the  shortening  reaction — what  does 
it  depend  on?) 


THE  DECEREBRATE  PREPARATION.  253 

With  everything  ready  to  take  a  graphic  record  of  the  move- 
ments of  the  left  leg,  the  Sherrington  electrodes  are  connected  on 
both  sides,  each  with  a  separate  inductorium,  and  the  recording 
drum  having  been  started  the  left  sciatic  is  stimulated  momentarily 
with  a  tetanising  current  of  moderate  strength.  The  leg  drops  into 
flexion  because  of  reflex  inhibition  of  the  postural  tonus.  Does  the 
leg  go  back  to  its  extended  position  when  the  stimulus  is  removed? 

A  similar  stimulus  is  applied  to  the  right  sciatic,  when  a  reflex 
contraction  of  the  left  extensor  muscle  will  occur  (crossed  extension 
reflex  (see  p.  240). 

Finally  it  can  be  demonstrated  that  this  reflex  contraction  is 
inhibited  through  stimulation  of  the  contralateral  sciatic  nerve. 
To  do  this  the  right  sciatic  is  stimulated,  and  whenever  the  tracing 
shows  that  the  left  extensor  muscles  are  decidedly  contracted,  the 
left  sciatic  is  simultaneously  stimulated  for  a  brief  period.  If  the 
proper  strength  of  stimulus  is  employed,  it  will  be  observed  that 
the  extensors  relax.  These  observations  should  be  repeated  with 
stimuli  of  varying  strengths  and  duration.  When  the  stimulation 
of  the  left  sciatic  is  discontinued  while  still  maintaining  that  of  the 
right  the  muscle  goes  back  to  the  contracted  state.  Draw  a  dia- 
gram to  show  the  probable  arrangement  of  the  reflex  pathways  in 
the  spinal  cord. 

DECEREBRATE  PIGEON. 

Demonstration  18.— While  under  the  influence  of  ether  the 
skull  is  exposed  by  a  transverse  incision  of  the  skin.  A  piece  of 
bone  just  large  enough  to  expose  the  cerebrum  is  quickly  removed 
by  sharp  scissors.  By  means  of  a  glass  tube  connected  with  a 
suction  pump*,  the  cerebrum  is  sucked  up.  Great  care  must  be 
taken  to  avoid  injury  to  the  cerebellum,  as  there  is  no  tentorium 
in  the  pigeon.  The  advantage  of  this  method  of  decerebration  is 
that  the  blood  is  sucked  away,  thus  allowing  a  clear  view  of  the 
field  of  operation.  The  cavity  is  plugged  with  absorbent  cotton, 
and  the  skin  sewn  up.  The  actual  decerebration  should  take  but  a 
few  seconds. 

*The  tube  should  be  slightly  drawn  out  with  an  opening  2  or  3  mm.  in  diameter. 
This  tube  is  connected  by  rubber  tubing  to  a  filter  flask  so  that  the  brain  tissue 
will  not  be  drawn  into  the  pump. 


254  EXPERIMENTAL  PHYSIOLOGY. 

The  operation  should  be  performed  at  least  two  or  three  hours 
before  the  observations  are  to  be  made  in  order  to  permit  complete 
recovery  from  the  ether. 

A  decerebrate  pigeon  has  no  memory,  therefore  no  sense  of  fear. 
Tt  is  not  conscious  of  painful  stimulation.  It  sleeps  unless  stimu- 
lated. It  starves  unless  food  is  placed  back  in  the  throat  so  that 
the  swallowing  reflex  is  started. 

Stimulate  the  pigeon  in  the  following  ways : 

1.  Push  it  in  order  to  get  it  to  move. 

2.  Produce  a  loud  sharp  sound  near  one  ear. 

3.  Allow  it  to  smell  strong  ammonia. 

4.  Stand  it  on  a  sheet  of  metal  and  gradually  heat  the  latter 
until  too  warm  for  your  own  hand. 

5.  If  the  bird  is  not  too  weak,  toss  it  into  the  air  and  it  should 
fly. 

Make  notes  of  the  behaviour  of  the  animal  in  response  to  these 
stimuli  and  explain  the  results. 


CHAPTER    XXXIX. 

THE  SPINAL  CAT  (SHERRINGTON'S  PREPARATION.) 

In  this  procedure  the  spinal  axis  is  cut  about  4  m.m.  behind  the 
point  of  the  calamus  scriptorius,  and  the  spinal  animal  exhibits  a 
considerable  number  of  complex  reflex  movements,  although  the 
arterial  blood  pressure  remains  low.  Spontaneous  respirations,  of 
course,  cease  entirely  so  that  it  is  necessary  to  apply  artificial 
respiration.  The  control  of  body  temperature  also  disappears, 
necessitating  artificial  warmth. 

Demonstration  19. — Anaesthetise  a  cat  deeply,  insert  a 
tracheal  cannula  low  down  and  ligate  the  carotid  arteries  on  both 
sides  of  the  neck.  Place  the  animal  in  the  prone  position  and 
holding  the  head  in  the  left  hand,  make  a  wide  transverse  incision 
through  the  skin  over  the  occiput  and  retract  the  skin  downward 
so  as  to  expose  the  muscles  of  the  upper  end  of  the  neck.  Feel  for 
the  transverse  processes  of  the  atlas  and  cut  the  muscles  across  at 
the  posterior  edges  of  the  processes.  Cut  off  the  spinous  process 
of  the  axis  with  a  bone  forceps.  Thread  a  large  packing  needle 
(at  least  15  cm.  long)  with  stout  string,  and  pass  it  close  under  the 
body  of  the  axis  (i.e.,  posterior  to  the  cesophagus)  and  tie  it  tightly 
in  the  depths  of  the  cross  cut.  This  ligature  compresses  the 
vertebral  arteries  as  they  pass  between  the  transverse  processes  of 
the  axis  and  atlas. 

The  animal  is  now  decapitated.  For  this  purpose  flex  the  head 
so  as  to  stretch  the  occipito-atloid  membrane,  and  thrust  the  point 
of  a  narrow  (12  mm.  wide)  amputation  knife  through  the  membrane 
moving  it  laterally  so  as  to  cut  the  cord.  With  the  point  of  the 
knife  resting  on  the  anterior  wall  of  the  spinal  canal  bend  the  head 
forcibly  to  one  side,  and  carry  the  edge  of  the  knife  through  the 
opposite  occipito-atloid  joint.  Repeat  this  procedure  for  the  other 
joint  and  then  complete  the  decapitation  by  cutting  through  the 
remaining  tissues.  If  there  is  bleeding  it  can  be  stopped  by  raising 
the  stump.  When  it  has  ceased,  bring  the  skin  flaps  together  over 
the  stump  and  lay  the  preparation  on  a  warmed  observation  table. 
Artificial  respiration  by  means  of  a  pump  connected  with  the 
tracheal  cannula  must  of  course  be  instituted  before  the  cord  is 

255 


256  EXPERIMENTAL  PHYSIOLOGY. 

severed,  if  not  before.  It  is  advisable  to  warm  the  air  from  the 
pump,  but  whether  or  not  this  is  done,  great  care  must  be  taken  to 
see  that  the  temperature  of  the  preparation,  observed  by  a  clinical 
thermometer  placed  in  the  rectum,  does  not  fall.  For  some  time 
after  the  decapitation  little  reflex  activity  is  shown  by  the  prepara- 
tion— why  is  this  the  case?  In  about  one  hour,  however,  many 
complex  reflex  movements  can  readily  be  elicited.  Of  these  the 
following  should  be  studied;  the  movements  may  be  recorded  by 
tying  threads  to  the  hind  limbs  and  connecting  with  reducing  levers. 

1.  THE  FLEXION  REFLEX,  by    applying  stimuli   (mechanical, 
electrical)  to  the  skin  of  the  foot  or  stimulating  the  central  end  of 
one  of  the  sensory  nerves  (peroneal)  with  the  tetanising  current. 
The  latent  time,  grading  of  intensity,  summation,  etc.,  may  he 
studied  by  the  procedures  already  described  on  p.  240. 

2.  THE  KNEE  JERK,  by  passively  flexing  the  knee  joint  and 
tapping  the  patellar  tendon.     The  prompt  and  limp-like  return 
of  the  leg  to  its  original  position  should  be  contrasted  with  the 
gradual  and  imperfect  return  observed  in  a  decerebrate  prepara- 
tion (p.  249) 

3.  THE  SCRATCH  REFLEX,  by  stroking  the  skin  at  the  side  of  the 
neck.     The  scratching  movement  of  the  homolateral  hind  limb  is 
not  so  easily  evoked  as  in  a  spinal  dog  that  has  recovered  from  shock, 
and  it  may  not  appear  until  the  decapitated  animal  has  been  par- 
tially asphyxiated  by  discontinuing  the  artificial  respiration  for  a 
minute  or  so.     Sometimes  the  preparation  shows  a  hyperexcitable 
scratch  reflex,  but  this  often  depends  on  inadequate  pulmonary 
ventilation.     When  it  occurs,  the  respiratory  apparatus  should  be 
examined  and  the  tracheal  cannula  cleared  of  any  mucus  that  may 
be  interfering  with  the  free  passage  of  air  into  and  out  of  the  lungs. 
If  the  scratch  reflex  is  marked,  its  inhibition  may  readily  be  demon- 
strated by  stimulating  the  central  end  of  the  peroneal  nerves  of 
either  leg. 

4.  STIMULATION  OF  THE  POSTERIOR  COLUMNS  OF  THE  SPINAL 
CORD,  by  exposing  the  upper  end  of  the  severed  cord  and  stimulating 
by  the  unipolar  method.     This  observation  is  of  value  because  it 
shows  that  stimuli  descending  by  the  main  sensory  pathways  of  the 
cord — 'because  the  fibres  transmit  in  both  directions  (cf.  p.  46) — flow 
into  the  collaterals  which  are  adjacent  to  the  point  of  entry  of  the 
fibres  into  the  cord.     To  make  the  observation,  place  an  indifferent 


THE  SPINAL  PREPARATION.  257 

electrode  on  one  foot  (well  moistened  with  strong  saline  solution) 
and  connect  its  wire  with  one  pole  of  the  secondary  coil  to  the  other 
pole  of  which  a  fine  stigmatic  electrode  is  attached.  Clear  away  any 
blood  clot  from  the  upper  end  of  the  cord  (using  a  moistened  camel's 
hair  brush)  and  while  holding  the  neck  stump  in  one  hand,  stimulate 
the  dorsal  columns  of  the  cord,  first  near  the  median  fissure  and 
then  as  near  as  possible  to  the  posterior  horn  of  grey  matter.  .  In 
the  former  case  it  is  the  homolateral  hind  limb  that  flexes,  in  the 
latter  case,  the  homolateral  fore  limb.  It  may  be  necessary  to 
repeat  the  observation  several  times  with  varying  strengths  of 
stimulation  in  order  to  secure  definite  results. 

5.  THE  FUNCTIONS  OF  THE  SPINAL  ROOTS,  by  removing  the  lam- 
inae and  articular  processes  of  the  lumbar  vertebrae.  The  procedure 
for  this  operation  is  in  general  the  same  as  that  described  for  the  dog 
(p.  245)  with  the  difference  that  the  spinous  processes  of  the  exposed 
lumbar  vertebrae  are  not  cut  at  their  bases,  but  the  laminae  are 
freely  exposed  by  cutting  away  the  muscles  which  lie  over  them. 
The  articular  processes  are  then  snipped  across  and  while  pulling 
up  the  lowermost  (7th)  spinous  process  with  a  strong  forceps,  the 
laminae  are  cut  through  beginning  with  the  7th  lumbar  and  working 
upwards.  The  ganglia  of  the  posterior  roots  are  brought  into  view 
by  picking  away  the  stumps  of  the  articular  processes.  The  7th 
ganglion  lies  on  a  line  with  the  iliac  crests. 

Finally  it  is  important  to  use  the  decapitate  preparation  to 
study  the  various  conditions  which  control  THE  ARTERIAL  BLOOD 
PRESSURE.  The  technique  is  the  same  as  that  already  described  for 
the  anaesthetized  dog  (p.  79)  only,  of  course,  small  cannulae  must 
be  used  and  the  pressure  established  in  the  tubing  which  connects 
cannula  to  manometer  prior  to  removal  of  the  clip  from  the  artery, 
must  not  be  more  than  about  50  mm.  Hg. 

There  are  certain  vascular  reactions  which  it  is  especially 
valuable  to  investigate  in  the  decapitate  preparation.  These  are: 

1.  The  effect  of  stimulation  of  the  spinal  cord  on  the  blood 
pressure. 

2.  The  effect  of  varying  amounts  of  epinephrin  injected  into  the 
femoral  vein. 

3.  The  effect  of  pituitary  extract  similarly  injected. 

4.  The  effect  of  asphyxia. 

This  last  group  of  observations  may  be  done  by  advanced 
students. 


SECTION     IX. 
GENERAL  PHYSIOLOGY. 

CHAPTER    XL. 

PROPERTIES  OF  LIVING  PROTOPLASM. 
CHEMICAL  CONSTITUENTS  OP     PROTOPLASM. 

In  the  broadest  sense  physiology  is  that  science  which  deals 
with  the  phenomena  of  living  matter  and  attempts  to  explain  these 
phenomena  in  terms  of  physics  and  chemistry.  To  the  majority 
of  people  physiology  means  in  reality  "human"  or  at  best  "mam- 
malian" physiology,  i.e.,  a  study  of  the  functions  of  the  human 
body,  or  where  this  is  not  possible  the  functions  of  the  dog  or  cat 
are  studied  with  the 'assumption  that  the  physiology  of  these 
mammals  is  comparable  with  our  own.  This  is  a  perfectly  natural 
concept  since  we  are  primarily  interested  in  ourselves,  and  are 
interested  in  other  living  things  only  as  they  have  some  reference 
to  ourselves — to  be  cultivated  if  they  work  for  our  good,  to  be 
guarded  against  if  harmful.  Recently,  however,  it  has  been 
demonstrated  that  light  may  be  thrown  on  many  problems  in 
human  and  mammalian  physiology  by  a  study  of  the  life  pro- 
cesses in  the  more  lowly  forms  of  the  animal  world,  and  of  the 
plant  world  as  well.  To  this  study  of  the  broader,  more  general 
aspects  of  the  functioning  of  living  material  in  any  form  wherever 
life  exists  has  been  applied  the  title  of  General  Physiology. 

I.  The  properties  of  living  protoplasm  as  shown  in  simple  plant 
animal  cells. 

Materials:  Spirogyra,  Elodea,  cells  of  onion  epidermis,  Para- 
mecia,  Amoebae  ,Stentor,  stamen  hairs  of  Tradescantia. 

A.  Examine  the  materials  provided  for  the  following  points: 
colour,  consistency,  optical  nature,  elasticity,  viscosity  and  other 
physical  characteristics.  Is  protoplasm  homogeneous?  What  is 
the  nature  of  the  inclusions?  What  does  the  shape  of  the  inclu- 
sions tell  one  as  regards  the  physical  state  of  protoplasm?  Crush 
the  cells  or  cut  them  in  two.  What  happens  to  the  protoplasm? 

258 


GENERAL  PHYSIOLOGY  259 

Compare  the  fluidity  of  the  animal  and  plant  cells  provided.  Does 
the  nucleus  differ  from  the  cytoplasm  in  optical  properties?  Try 
the  effect  of  acetic  acid  if  the  nucleus  is  not  clearly  distinguishable 
in  the  living  condition.  What  evidence  can  you  obtain  that  there 
is  an  external  living  membrane  present?  Compare  the  plant  and 
animal  cells  in  this  regard. 

B.  If  there  is  movement  within  the  cells  describe  this  "cyclosis" 
in  detail,  making  diagrams  to  show  the  directions  in  which  the 
granules  move.     Does  the  movement  follow  definite  lines?     Com- 
pute the  rate  in  millimetres  per  second  of  the  protoplasmic  move- 
ment in  Elodea,  or  Tradescantia  at  room  temperature,  by  means  of 
an  ocular  micrometer  and  stopwatch.     It  is  a  rule  that  the  speed 
of  chemical  reactions  is  doubled  with  each  rise  of  10°  C.  (Van't 
HofFs  rule).     This  is  expressed  by  the  equation,  Qi0  =  2.     For  a 

10 

/  IT-\'- 

range  of  less  than  10°  C.  the  following  formula  is  used :  Q 

where  KI  =  initial  rate,  and  K2  the  final  rate  of  the  reaction/ ti  = 
the  original  temperature,  and  t2  the  final  temperature.    Does  living 
protoplasm  obey  this  rule?     Plot  a  heat  curve  containing  at  least 
four  points  for   (1)   a  plant  cell  exhibiting  striking  protoplasmic 
movement,  (2)  contraction  of  the  vacuoles  in  the  paramecium,  and   ^ 
(3)   the  pulsations  of  the  dorsal  blood  vessel  of  the  earthworm.    'i 
What  is  the  highest  temperature  from  which  the  cells  will  recover    cS*- 
after  an  exposure  of  3  minutes?    What  changes  in  the  appearance  '5    ' 
of  the  protoplasm  occur  above  this  temperature?     (Consult  Bayliss  "  j*- 
General  Physiology  pp.  41-45).  j*^ 

C.  What  is  the  effect  of  various  concentrations  (N/10,  N/100,^  t 
N/1000,  etc.),  of  acids  (e.g.,  acetic,  HC1),  bases  (NH4OH,  NaOH),      •" 
salts  (NaCl,  CuSO4,  HgCl2),  anaesthetics  (alcohol, ether,  chloroform) 
sugar,  iodine,  etc.,  on  the  movements  of  protoplasm  and  on  the 
physical   state   of   the   protoplasm?      In   what  ways   do   Stentor, 
Paramecia,  and  Amoeba  each  attempt  a  defense  against  a  harmful 
agent?     Can  you  give  an  explanation  of  this  action  on  purely 
physical  or  chemical   (non-anthropomorphical)   grounds? 

D.  Plasmolysis  is  the  shrinking  of  the  protoplasm  in  a  plant 
cell  from  its  cellulose  wall.     Is  the  cellulose  wall  living?    What  is 


the  part  of  the  plant  cell  that  is  homologous/with  the  outer  living 
^     lyiembrane  in  the  amoeba?     Determine  the/osmotic  pressure  of  a 
lant  cell  by  rinding  a  concentration  of(KNOj)which  just  fails  to 
lasmolyse  the  cell  in  half  an  hour.     Determine  the  osmotic  pres- 
ure  of  the  red  corpuscles  of  the  frog  by  finding  the  solution  of 
NaCl  which  will  neither  cause  the  cells  to  shrink  nor  to  swell. 
Does  all  protoplasm  have  the  same  osmotic  pressure?    How  would 
you  expect  the  osmotic  pressure  of  fresh  and  salt  water  plants  to 
compare?     (Bayliss,  Prin.  of  Gen.  Phys.,  pp.  162-165). 

E.  What  is  the  effect  of  the  electric  current  on  living  protoplasm? 
Use   plant   cells   showing  streaming   movements,    Paramecia   and 
Amoebae.     Note  particularly  the  effect  on  the  cilia  of  the  Para- 
mecia.   To  which  pole  do  the  Paramecia  move?    Can  you  explain 
the  movements  of  the  Paramecia  in  an  electric  current  in  non- 
anthropomorphic    terms?      (Jennings,    Behavior    of     the     Lower 
Organisms,  Chap.  V.). 

F.  Study  the  locomotion  of  the  Amoeba.    How  are  pseudopodia 
formed?    Does  the  animal  move  in  any  one  direction,  or  are  its 
movements  at  random?     Touch  the  amoeba  with  a  fine  glass  rod  at 
what  may  be  considered  for  the  moment  the  anterior  edge.    Where 
does  the  next  pseudopodium  appear?     Are  the  pseudopodia  ever 
wrinkled?    (Jennings,  Behavior  of  the  Lower  Organisms,  Chap.  I). 
Construct  a  trough  by  fastening  a  coverslip  on  each  side  of  a  glass 
slide  with  Canada  balsam.    Observe  in  this  trough  with  the  micro- 
scope  stage   vertical   the   movements   of   the   Amoeba   in   profile. 
Notice  the  shape  of  the  Amoeba  as  it  falls  freely  through  the  water. 
(Dellinger,  Jour.  Expt.  Zool.,  1906). 

Have  you  discovered  in  these  examples  of  protoplasm  any 
evidences  (1)  of  irritability,  i.e.,  the  capability  of  receiving  im- 
pressions from  the  outside  world — shown  so  markedly  in  our  sense 
organs;  (2)  of  conduction,  i.e.,  the  capability  of  transmitting  effects 
of  stimuli  to  parts  remote  from  the  point  of  stimulation — shown  in 
our  nerves;  (3)  of  contractibility,  as  in  our  muscles,  etc.?  In  other 
words,  can  it  be  said  that  there  are  inherent  in  protoplasm  itself 
as  a  physico-chemical  complex  the  possibilities  for  all  the  specialized 
functions  we  find  in  living  beings,  such  as  the  eye  and  brain  of 
man,  or  the  swiftly  moving  wing  of  the  bee?  And  is  the  explanation 
of  these  characteristics  of  protoplasm  beyond  the  realm  of  physical 
and  chemical  laws?  (Bayliss,  Prin.  of  Gen.  Phys.,  p.  3-4). 


GENERAL  PHYSIOLOGY        O  *?    ?  ? 

,     «      -    « 

//.   Chemical  constituents  of  Protoplasm. 

A.  Chemical  elements  necessary  to  life  and  growth- 
Complete  water  culture  for  seedlings  contains  the  following: 

KNO3          1  gm. 

MgSO4        0.5gm. 

CaSO4         0.5gm. 

KH2PO4      O.ogm. 

NaCl  0.5gm. 

NaCl3          3-4  drops  of  10%  soln. 

Dist.  H2O  1000  c.c.— Solution  to  be  heated  to  100°  C.  for 

5  minutes. 

Certain  members  of  the  class  will  make  up  the  whole  solution 
for  control,  others  will  omit  one  element.  Compare  the  rate  of 
growth  and  general  appearance  of  seedlings  with  roots  placed  in 
the  different  solutions  during  a  period  of  several  weeks.  What  is 
the  apparent  function  of  each  element  in  the  medium?  What  is 
the  source  of  carbon? 

B.  The  more  important  elements  in  protoplasm — 

1.  Carbon—substance   chars   upon   heating   in   dry   test   tube 
(flour,  sugar,  bean,  etc.). 

2.  Hydrogen — heat  dried  material  as  for  carbon  and  note  con- 
densation of  H2O  in  upper  part  of  tube.    (Flour,  bean,  etc.). 

3.  Oxygen— dry  material;  test  tube  closed  with  cork  having 
two  holes;  glass  tube  through  one  hole  to  end  of  tube  and  connected 
with  gas  jet;  the  other  connects  with  Bunsen  burner.     Pass  gas 
through  the  tube  until  the  air  is  displaced.     Light  the  burner  and 
heat  the  tube.     The  hydrogen  is  burned  to  H2O  by  O2  in    the 
material.      (Flour). 

4.  Nitrogen — heat  with  soda-lime — NH3  is  given  off.    Test  by 
its  action  on  litmus  and  cone.  HC1.     (Flour,  bean,  etc.). 

5.  Sulphur — -boil  with  strong  HNO3.     Dilute  and  filter  if  neces- 
sary— BaCl2  gives  white  precipitate  of  BaSO4.     (Flour,  white  of 
egg). 

6.  Phosphorus — to    half    of    above    solution    add    ammonium 
molybdate  and  heat.    Yellow  ppt.  indicates  P.     (Flour,  etc.). 

C.  The  chief  way  in  which  these  elements  are  combined    in 
protoplasm. 


262  EXPERIMENTAL  PHYSIOLOGY. 

1.  Carbohydrates. 

(a)  Test  cane  sugar  with  Fehling's  Soln. — Boil  with  dil.  HC1 
and  repeat  test. 

(b)  Molisch  reaction.     Place  5  c.c.  con.  H2SO4  in  a  test  tube. 
Incline  this  tube  and  pour  in  gently  5  c.c.  of  solution  to  be  tested 
to  which  two  drops  of  Molisch's  reagent  has  been  added.    Red   to 
violet  zone  at  point  of  contact  of  the  two  liquids  indicates  a  sugar. 

2.  Protein. 

(a)  Xanthoproteic  Reaction.    Add  cone.  HNO3.   Heat.    Cool- 
should   turn   yellow — add   NHUOH   carefully   in   excess.      Yellow 
deepens  to  orange.     Use  egg  white  coagulated. 

(b)  Biuret.     Add  cone.   KOH,  mix  thoroughly  and  add  few 
drops  dilute  CuSC>4.    Purple  or  violet  colour  indicates  protein.   Use 
egg  white. 

3.  Fats. 

Rub  butter,  suet,  and  a  peanut  or  walnut  kernel  on  a  piece 
of  ordinary  writing  paper.  A  translucent  spot  appears.  This  is 
not  removed  by  heating  (cf.  essential  oils  as  oil  of  cloves,  winter- 
green,  etc.),  nor  will  it  wash  off  with  water  (cf.  glycerine). 

D.  Test  samples  of  the  various  foods  which  go  to  make  up  an 
average  meal,  e.g.,  bread,  meat,  potatoes,  a  vegetable,  etc.,  for 
the  three  classes  of  foods.  Write  the  results  in  the  form  of  a  table 
indicating  presence  by  +,  absence  by  — . 


" 


CHAPTER    XLI. 
PHYSICAL  CHEMISTRY  OP  CELLS. 

Physical  chemistry  of  cells. 

A.  Diffusion  rates  in  non-living  material.     (1)  Invert  a  tube  of 
H2O  containing  a  few  drops  of  phenolphthalein  in  a  dish  of  dilute 
KOH.     Note  the  rate  at  which  the  liquid  in  the  tube  turns  red. 
(2)  Repeat  with  a  tube  of  solid  agar  to  which  phenolphthalein  has 
been  added.     (3Hm^4^aatA>£^Leolidified  ctareh  pa^tc  in  a  oolu-??' 
.tion  of  IKTrernhttoterraU'  uf  change  uf  mkmr.    Does  the  physical     " 
character  of  the  reagents  affect  the  rate  of  diffusion?  fir 


B.  Semi-permeable    membranes    in    living    cells.      (1)     Place 
Spirogyra,  Elodoea  and    Paramecia  in  a  very  dilute  solution  of  a*xr 
neutral  red  (one  drop  to  a  watch  glass  of  water).     Describe  the 
phenomena.    (2)  Try  more  concentrated  solutions.    (3)  Place  living 
material  stained  with  neutral  red  in  N/40  NaOH,  Ba(OH)2  and 
NHUOH.     Record  the  time  for  colour  change.      Return  to  H2O 
after  colour  change  has  taken  place.     Is  there  a  return  to  the 
original  condition?    Have  any  cells  been  killed?    To  which  solution 

is  the  material  most  permeable?  (4)  Repeat  with  cells  killed  by 
heat  or  exposure  to  chloroform.  (5)  Wash  small  cubes  of  beet  in 
running  H2O  to  remove  the  coloured  material  in  broken  or  injured 
cells.  Heat  one  half  to  them  to  boiling.  Compare  the  rate  of 
diffusion  of  the  red  pigment  in  the  boiled  and  raw  cubes.  How 
do  you  account  for  this  difference  in  permeability  of  living  and 
dead  cells?  (6)  Place  washed  cubes  of  beet  in  1.82%  NaCl  (  =  0.31 
molar)  which  is  isotonic  with  the  cell  contents.  Note  result. 
Explanation?  (7)  Place  similar  washed  cubes  in  a  salt  solution  also 
containing  0.17%  CaCl2  made  in  the  following  manner:  take  a 
3.64%  solution  NaCl  and  add  an  equal  volume  of  0.34%  CaCl2. 
Explain  the  result. 

C.  Artificial  membranes.     (1)  Float  minute  crystals  of  CuSC>4 
on  a  2%  solution  of  K4Fe  (CN)6.    Describe  results  fully.      Is  there 
a  suggestion  of  growth?     (2)  Try  the  reverse,  a  crystal  of  K4Fe 

263 


4*wu&» 

264  EXPERIMENTAL  PHYSIOLOGY. 

(CN)6  in  a  3%  CuSO4  solution.  (3)  Place  a  lump  of  fused  CaCl2 
in  a  jar  filled  with  saturated  Na2CO3.  Follow  appearance  daily 
if  possible.  (4)  Shake  CHC13  with  egg  albumen.  Examine  under 
microscope.  The  result  is  a  collection  of  artificial  cells  each  sur- 
rounded by  a  film  of  protein. 

D.  Osmosis.     Prepare  collodion  bags  in  the  following  manner. 
Pour  5  c.c.  of  the  dissolved  collodion  into  an  absolutely  clean 
short  test  tube.     Invert  the  test  tube  over  the  bottle  of  collodion, 
allowing  as  much  of  the  collodion  to  run  back  into  the  bottle  as 
will  do  so.    Now  rotate  the  test  tube  in  the  air,  still  inverted,  until 
the  collodion  is  no  longer  liquid.    Withdraw  the  ether  vapour  from 
the  tube  by  suction.     Finally  introduce  some  water  into  the  test 
tube,  loosen  the  collodion  membrane  from  the  sides  of  the  tube 
and  transfer  the  collodion  bag  to  water.    Fill  one  bag  with  molasses 
and  tie  to  a  long  glass  tube.    Suspend  in  H2O  and  mark  the  height 
to  which  the  liquid  rises.    Note  rate  of  rise.    Do  the  same  with  egg 
albumen,  2  M  sugar  solution  and  2  M  NaCl.      Recall  in  this  con- 
nection experiments  already  performed  on  Spirogyra,  etc.     How 
do  you  account  for  the  difference  in  behaviour  of  sugar  and  salt 
solution  of  the  same  molecular  concentration?    Calculate  from  the 
"gas  laws"  the  height  to  which  a  2  M  solution  of  cane  sugar  should 
rise  if  the  colloidal  bag  w^ere  absolutely  impermeable  to  sugar,  and 
freely  permeable  to  water. 

E.  Surface  tension.     (1)  Float  a  needle  on  the  surface  of  H2O. 
(2)  Repeat  with  a  soap  solution.     (3)  What  is  the  form  of  drops  of 
H2O  falling  from  a  pipette?    Why?     (4)  Make  a  loop  of  wire  and 
attach  to  this  a  smaller  loop  of  fine  silk.     Form  a  film  on  the  wire 
frame  with  soap  solution.     Wet  a  needle  with  soap  solution  and 
pass  through  the  film.     Is  the  film  ruptured?     May  this  have  any 
relation  to  the  passing  of  leucocytes  through  walls  of  capillaries? 
Puncture    the    film    within     the    silk    loop.      Result?     Explain. 
(5)  Plateau's  expt.— 10  cc..  60%  alcohol  in  test  tube.    Add  a  drop  of 
olive  oil  (which  should  sink;  if  it  does  not,  add  70%  alcohol).   Add 
a  small  amount  of  50%  alcohol  without  stirring,  then    a  drop  of 
olive  oil  (which  should  not  sink;  if  it  does,  add  more  50%  alcohol.) 
Find  the  mixture  in  which  olive  oil  drops  will  sink  part  way  but 
not  entirely  to  bottom.     What  is  the  form  of  the  drops?    Try  to 
change  that  shape  with  a  glass  rod.     Result?     Is  there  any  differ- 


PHYSICAL  CHEMISTRY  OF  CELLS  265 

ence  in  this  regard  between  large  and  small  drops?    Wet  the  glass 
rod  with  NaOH  and  repeat  the  experiment.     (6)   Drop  a  small 
amount  of  paraffin  oil  in  70%  alcohol.     Increase  the  surface  of 
the  oil   by   pulling  out   projections  with   a  glass  rod.     Results? 
Explain.      (7)  Float  a  clean  rubber  band  on  surface  of  clean  water. 
Touch  water  inside  the  band  with  rod  moistened  with   olive  oil. 
Result?    Touch  the  water  outside  band.     Explanation.     (8)  Place 
a  crystal  of  camphor  on  water.    Trace  the  direction  of  the  move- 
/  ments.    Touch  the  surface  with  a  glass  rod  moistened  in  oil.    Does 
y    this  action  bear  any  resemblance  to  living  phenomena?     (9)  Place 
a  drop  of  Hg.  in  a  watch  glass.    Note  the  form  and  size.    Cover  it 
,with  2%  HNO3  and  place  a  crystal  of  K2Cr2O7  1  cm.  away  from 
it.     Draw  changes  in  shape  of  Hg.     Compare  with  the  behaviour 
^D  of   amoeba.     (10)  Prepare   a   cell  as  follows:  with  balsam  fasten 
*       small  glass  rods  to  a  slide  at  such  a  distance  from  each  other  that 
they  will  support  a  cover  glass.     When  dry,  fill  the  cell  with  a 


Xjbmi 


ixture  of  2  parts  glycerine  to  one  of  70%  alcohol.  Place  on  the 
>ver  glass.  Introduce  under  the  glass  with  a  capillary  tube  one 
Js  small  drop  of  clove  oil.  Result?  (The  drop  should  behave  like 
an  amoeba).  Now  touch  the  cover  glass  with  a  hot  wire  or  glass 
rod.  Result?  (11)  Into  a  drop  of  chloroform  on  a  slide,  introduce 
the  end  of  a  small  glass  rod  (1  cm.  long).  Result?  Repeat,  using 
rods  dipped  in  shellac,  paraffin,  gum  arabic,  NaCl,  sugar.  Does 
this  resemble  "choice"  of  food  in  amoeba?  Can  you  get  the  drop 
of  CHC13  seemingly  to  "ingest"  "digest"  and  "excrete"?  (12) 
Artificial  amoeba.  Wet  a  piece  of  cardboard  in  one  spot,  1  cm.  in 
diameter,  with  water.  Cover  this  cardboard  with  olive  oil,  letting 
the  oil  soak  into  the  paper  everywhere  except,  of  course,  at  the 
wet  spot.  Remove  the  surplus  of  oil  and  lay  the  cardboard  flat 
on  the  table.  Place  a  drop  of  glycerine  mixed  with  soot  on  the 
cardboard  at  the  edge  of  the  spot  where  the  water  was.  Study 
the  movements  and  draw.  Can  you  satisfactorily  explain  pseudo- 
podial  movement  as  due  entirely  to  surface  tension  effects? 

Colloids. 

(1)  Effect  of  electrolytes  on  the  swelling  of  gelatin.  Soak  a 
sheet  of  gelatin  in  water.  With  a  cork  borer  cut  out  discs  of  known 
size  and  place  them  in  a  series  of  concentrations  of  acids,  bases, 


266  EXPERIMENTAL  PHYSIOLOGY 

and  salts,  N,  N/10,  N/20,  N/30,  N/40,  N/50.  Use  discs  in  dis- 
tilled water  for  control.  Let  them  stand  for  several  hours  in  these 
solutions,  then  measure  the  size  of  each.  Tabulate  the  results 
for  the  whole  series  of  all  reagents.  (Some  members  of  class  use 
HC1,  others  H2SO4,  NaCl,  Na2SO4,  NaOH,  NH4OH,  etc.).  What 
is  the  optimum  for  each  electrolyte?  Does  valency  have  any 
effect?  Antagonistic  solutions  should  also  be  tried,  especially  the 
following:  N/10  HC1  +  N/10  NaCl  (add  equal  quantities  of  N/5 
solution  of  each);  N/20  HC1+N/10  NaCl;  N/10  NaOH  +  N/10 
NaCl;  N/20  NaOH+N/10  NaCl. 

Another  method,  perhaps  better  than  the  disc  method,  is 
to  arrange  a  series  of  test  tubes  of  uniform  size  each  containing 
the  same  quantity  of  powdered  gelatin  (0.5  —  1  gm.).  10  c.c.  of 
the  given  solution  is  added  and  when  the  swelling  has  become 
constant  the  height  of  the  column  of  gelatin  is  read. 

(2)  Brownian  movement.^.  Rub  a  piece  of  a  water-colour 
tablet  in  water  on  a  slide  and  examine  under  high  power  both  with 
reflected  and  transmitted  light  (dark  field).  Can  you  trace  the 
path  of  a  single  particle?  How  would  you  distinguish  one  of  these 
colloidal  particles  from  a  typhoid  bacillus,  for  example?  Add  a 
drop  of  warm  (liquid)  gelatin  to  the  water-colour.  Result?  Allow 
the  gelatin  to  cool  and  harden.  Result  on  Brownian  movement? 


(1)  Filter  solution  of  methylene  blue  or  congo  red  through  bone 
charcoal.  The  filtrate  should  be  colourless.  Now  pour  through 
the  charcoal  95%  alcohol.  The  colour  should  pass  through.  Can 
you  account  for  this  action  on  the  supposition  of  changes  in  the 
electric  charges  on  the  aggregates  of  molecules?  (2)  Place  suc- 
cessive drops  of  different  dyes  on  the  centre  of  a  circular  filter 
paper.  Explain  results. 


CHAPTER   XLII. 
ENZYMES  AND  DIGESTION.     BUFFERS. 

IV.  Enzymes  and  Digestion. 

1.  Ptyalin   from   saliva,      (a)    Test   a   biscuit   for   sugar  with 
Fehling's  solution.    Chew  a  biscuit  until  it  tastes  sweet.    Now  test 
with  Fehling's.      Explain  result,     (b)  Collect  a  few  c.c.  of   saliva 
in  a  beaker  (the  flow  of  secretion  may  be  accelerated  by  chewing 
paraffin) ;  dilute  the  saliva  with  about  5  vols.  H2O.     Make  the 
following  mixtures:  (1)  equal  vols.  starch  paste  and  saliva,  (2)  the 
same,  except  using  saliva  that  has  been  previously  boiled,  (3)  same 
as  (1)  +5  drops  10%  HC1,  (4)  same  as  (1)  +5  drops  10%  KOH. 
Divide  (1)  into  two  portions  and  set  one  outside  window.    Warm 
all  the  other  mixtures  to  37°-40°  C.  (not  higher)  and  maintain  at 
40°  C.  for  10  minutes.    Test  each  mixture  for  starch  (using  iodine) 
and  for  sugar  (Fehling's).     Discuss  your  results. 

2.  Pepsin.    Prepare  12  Mett's  Tubes  of  egg-white  in  the  manner 
demonstrated.     Prepare  test-tubes  containing:  (a)   1%  pepsin  in 
1%  Na2CO3.     (b)  1%  pepsin  in  0.03  N  HCL.     (c)  1%  pepsin   in/ 
H2O.    To  each  of  these  add  a  Mett's  Tube  and  try  effect  on  each  ^ 
combination  of   (a)  cold  (out  of  window),    (b)  room   temperature,^ 

(c)  40°  C.    (d)  100°  C.  for   10  minutes  then  40°  C.    Make  quanti-     T! 
tative  estimations  at  different  time  intervals.     Results. 

3.  Coagulating  Enzymes.    Rennin.    Prepare  (a)  5  c.c.  fresh  milk    */ 
+  0.03  N  HCL  until  a  ppt.  formed,      (b)  5  c.c.  fresh  milk+5  drops    fi< 
rennin.    (c)  5  c.c.  fresh  milk+5  drops  rennin  +  5  drops  1%  Na2CO3.  >^e 

(d)  5  c.c.  fresh  milk+5  drops  0.03  N  HCL.    Let  stand  for  one  hour    A 
and  compare:   (a)  is  for  control  to  compare  with  (d).,   Try  (a)  after 
boiling  rennin. 

4.  Oxidizing  Enzymes.     Add  H2O2  to  blood.     Is  the  presence 
of  catalase  shown?     Try  bits  of  spleen,  liver,  lung,  kidney  and 
muscle  of  frog.    Which  gives  greatest  catalytic  action?    Boil  each 
of  these  tissues  and  repeat.    Add  solution  of  guiacum  to  a  slice  of 
potato.     Blue  colour  indicates  "active"  oxygen.     In  what  part 

267 


268  EXPERIMENTAL  PHYSIOLOGY 

of  the  potato  is  this  most  evident?  To  bits  of  potato  in  an  atmo- 
sphere of  coal  gas  (free  from  oxygen)  add  (without  admission  of 
oxygen)  a  few  drops  of  guiacum.  Should  be  no  colour  —  Why? 
Now  admit  air.  Result? 

5.  Is  digestion  in  protozoa  comparable  to  that  in  man?     Test 
alizarin  in  acid  and  alkali   to  determine  colour  changes.     Feed 
paramecia  with  a  suspension  of  alizarin.     Shortly  after  ingestion 
the  globule  of  alizarin  should  indicate  digestion  in  an  acid  medium. 
In  what  region  of  the  animal  does  this  take  place?     Later  in  the 
course  of  cyclosis,  an  alkaline  medium  may  be  shown. 

6.  Write  a  statement  concerning  the  characteristics  of  enzymes 
brought  out  in  these  experiments. 

V.  Buffer  action  and  determination  of  PH. 
Titrate  N/10  NaOH  against  N/10  HC1.     Do  the  same  with 


i  anS  N/10  NaHCO3  and  N/10  Na2CO3.     How  do 


you  account  for  the  differences  obtained?  (Bayliss,  Prin.  Gen. 
Phys.,  p.  203-205). 

Place  on  a  slide  small  bits  of  ciliated  epithelium  from  each  of 
three  regions  of  a  frog's  mouth,  anterior,  middle,  and  posterior. 
Find  the  concentration  of  acetic  acid  which  will  stop  the  movement 
of  the  cilia  in  the  anterior  piece  in  three  minutes.  This  can  be 
done  by  diluting  one  drop  of  a  stock  solution  of  acetic  acid  with  a 
definite  number  of  drops  of  distilled  water.  Note  the  time  when 
the  ciliary  motion  ceases  in  each  of  the  other  two  pieces.  Place  1  c.c. 
of  the  solution  of  acetic  acid  which  stops  ciliary  action  in  the 
anterior  piece  in  three  minutes  in  a  Pyrex  narrow-bore  tube,  add 
a  few  drops  of  an  appropriate  indicator  (brom-phenol  blue)  and 
match  the  resulting  colour  with  the  appropriate  colour  in  the  colour 
chart  of  Clark's  "  Determination  of  Hydrogen-Ions",  page  40. 
This  will  give  you  the  pH  of  the  solution. 

Repeat  using  HC1  as  the  acid,  and  thymol  blue  as  indicator. 

What  is  the  relation  of  acids  to  ciliary  movement?  Is  there  any 
difference  in  the  effectiveness  of  organic  and  inorganic  acids,  or  is 
the  hydrogen-ion  concentration  the  only  factor?  .  How  do  you 
account  for  the  fact  that  cilia  from  the  more  anterior  regions  are 
more  susceptible  to  the  acid? 


J    /* 

>/     U^L^U^ 

/      / 


CHAPTER  XLIII 
MOVEMENT,  ENVIRONMENT. 

Physiology  of  Movement. 

1.  Review  the  phenomena  of  amoeboid  movement  (I,  F,  etc.). 

2.  Review  ciliary  action  (V). 

3.  Muscle-nerve  physiology  (selected  experiments  from  Section  I) . 

Responses  of  Organisms  to  Environment,  Regeneration. 

The  functional  unit  of  the  nervous  system  in  multicellular  animals 
is  the  reflex  arc.  This  consists  in  its  simplest  form  of  a  receptor, 
an  afferent  nerve,  an  efferent  nerve,  and  an  effector.  In  verte- 
brates, for  example,  the  receptor  is  a  sense  organ  like  the  eye, 
which  is  affected  more  readily  by  a  certain  stimulus  than  are  the 
other  sense  organs.  The  change  wrought  in  this  sense  organ  by 
the  stimulus  affects  the  afferent  nerve  in  such  a  way  that  a  nervous 
impulse  is  initiated  and  passes  along  the  afferent  nerve  to  the 
central  nervous  system.  Usually  the  impulse  passes  over  an  inter- 
mediate neurone  before  it  reaches  the  efferent  neurone.  From  the 
efferent  neurone  the  impulse  passes  to  some  gland,  or  muscle,  the 
effector,  which  acts  in  its  own  characteristic  fashion. 

A.  Experiments  from  Section  III  will  be  selected  to  illustrate 
reflex  arcs  and  the  functions  of  the  central  nervous  system  of  the 
frog  as  an  example  of  a  vertebrate,  and  from  Section  V  to  illustrate 
the  action  of  receptors. 

B.  Invertebrates  are  more  stereotyped  in  their  reactions,  and 
their  responses  to  external  stimuli  are  often  constant  and  invari- 
able.    To  these  responses  has  been  applied  the  term  "tropisms" 
(also  " taxes").     (Consult  Loeb  " Forced  Movements,  Tropisms, 
and  Animal  Conduct"). 

The  material  to  be  studied  is  the  flat  worm,  Planaria  maculata. 
Note  methods  of  locomotion  (1)  on  flat  surface  under  water,  (2)  on 
the  surface  film,  (3)  in  air.  Does  the  animal  ever  swim  freely? 
Is  the  entire  ventral  surface  in  contact  with  the  substrate  during 

269 


270  EXPERIMENTAL  PHYSIOLOGY 

creeping?  Are  any  muscular  movements  observable  during  creep- 
ing which  may  account  for  locomotion?  (To  be  observed  under  (2) 
above).  Can  ciliary  action  account  for  locomotion?  Notice  the 
movements  of  the  auricles,  the  triangular  projections  lateral  to 
the  eyes.  Is  there  ciliary  movement?  Test  with  powdered  carmine. 

With  a  hair  or  other  delicate  instrument  explore  various  regions 
of  the  body  for  sensitivity  to  touch  and  determine  the  order  of 
sensitivity.  Touch  the  tip  of  the  head  with  a  blunt  needle.  If  done 
carefully  the  planarian  will  grip  the  needle  and  can  be  lifted  through 
the  water.  Response  to  touch  is  called  thigmotropism,  positive  if 
the  organism  moves  toward  the  source  of  stimulation  or  remains 
attached  to  it,  negative  if  the  organism  turns  or  moves  away.  If  there 
is  no  response  the  organism  is  said  to  be  indifferent  to  that  stimulus. 

Stereotropism.  Do  planarians  collect  in  cracks  with  as  much 
of  their  bodies  touching  the  dish  as  possible? 

Chemotropism.  Place  a  small  bit  of  liver  an  inch  or  so  away 
from  a  shaded  quiescent  planarian.  Describe  movements  of  animal 
in  finding  the  liver,  and  during  ingestion  of  food  note  action  of 
pharynx.  Is  there  any  circulation  of  ingested  food? 

Geotropism.  Do  you  find  any  difference  in  response  to  gravity 
depending  on  whether  the  animal  is  fed  or  not?  Be  careful  to  rule 
out  any  effect  of  light.  (Olmsted,  Jour.  An.  Behaviour,  1917). 

Galvanotropism.  Are  the  planarians  forced  to  travel  to  the 
anode  or  cathode?  Explanation? 

Rheotropism.  Do  planarians  move  up  or  down  stream  in  a 
gentle  current? 

Phototropism.  Place  five  worms  in  a  dish  one  half  of  which  is 
shaded,  the  other  half  brightly  illuminated.  Make  five  trials  and 
note  where  the  worms  collect  after  five  minutes.  Are  they  nega- 
tively or  positively  phototropic?  Use  coloured  glass  over  the 
illuminated  half,  e.g.,  blue,  red,  green,  yellow.  Differences  in 
response?  Throw  a  narrow  shadow  down  the  middle  of  the  dish 
and  start  a  planarian  moving  toward  the  source  of  light.  Can  you 
make  the  animal  continue  to  move  in  this  direction?  Describe 
movements.  Cut  a  worm's  head  off  just  behind  the  eyes.  Describe 
the  responses  of  each  piece  to  the  light.  Are  the  ey/^  essential 
for  the  light  response?  (Consult  article  by  Taliaferro  in  Jour. 
Expt.  Zool.  1921). 


MOVEMENT,  ENVIRONMENT  271 

Do  any  parts  exhibit  greater  permeability  for  dyes  than  other 
parts?  Use  methylene  blue.  (MacArthur). 

Students  will  be  divided  into  groups  to  work  out  the  answers 
to  the  following  questions:  (1)  Will  transverse  pieces  from  any  part 
of  the  body  regenerate  an  entire  new  animal.  (2)  Will  longitudinal 
strips  regenerate  entirely?  (3)  Will  obliquely  cut  pieces  regenerate? 
(4)  On  an  obliquely  cut  piece  which  eye  regenerates  first?  (5)  Can 
the  protrusible  pharynx  regenerate?  (6)  What  is  the  smallest 
proportion  of  the  body  which  will  regenerate?  (7)  How  do  small 
triangular  pieces  from  the  side  of  the  body  regenerate?  (8)  Is 
regeneration  more  rapid  in  the  light  or  in  the  dark?  (9)  What  is 
the  effect  of  starvation  on  the  size  of  the  worm?  (10)  Can  you  get 
double-headed  or  tailed  forms  by  splitting  the  head  or  tail? 

C.  Recall  the  experiments  in   I   illustrating  the  behaviour  of 
Protozoa  to  their  environment. 

D.  Responses  in  a  plant.      Touch  the  different  organs  of  the 
Sensitive  Plant,  Mimosa,  with  varying  degrees  of  strength.    Deter- 
mine the  rate  at  which  the  impulse  travels  along  a  frond  in  cms. 
per  sec.    Compare  this  with  conduction  in  the  frog  and  mammalian 
nerve.     Note  the  pulvinus  at  the  base  of  each  frond  and  leaflet. 
Can  you  account  for  the  action  of  the  plant  on  the  assumption  of 
osmotic  changes? 

E.  The  fundamental  differences  between  plants  and  animals. 
The  fundamental  difference  between  plants  and  animals  does  not 
consist  in   powers  of  movement,   since  many  plants  are  motile, 
e.g.,  algae,  while  many  animals,  e.g.,  corals,  are  sessile,  nor  in 
any  other  obvious  external  character.     The  difference  lies  in  the 
fact  that  plants  manufacture  their  food  from  raw  materials  using 
CO2  and  H2O  to  form  carbohydrates,  nitrates  as  a  source  of  protein 
nitrogen,  etc.    Animals  are  unable  to  do  this.     Once  the  requisite 
materials  are  made  up  into  the  proper  compounds,  the  process  by 
which  energy  is  liberated  for  the  carrying  on  of  life  is  essentially 
the  same  in  plants  and  animals,  i.e.,  respiration  is  common  to 
both.     Plants  are  unique  in  their  powers  to  form  materials  which 
store  up  energy.     Chief  of  these  processes  is  photo-synthesis,  the 
production  of  carbohydrates  from  CO2  and  H2O  by  means  of  the 
energy  of  sunlight. 

(1)   Place  an  equal  number  of  Planaria  of  the  same  size  in  each 


272 


EXPERIMENTAL  PHYSIOLOGY 


of  two  pyrex  glass  tubes  filled  with  water  containing  a  few  drops 
of  phenolsulphonephthalein.  Determine  the  pH  of  the  water  by 
comparing  with  known  standards.  Tap  water  is  slightly  alkaline. 
The  tubes  should  be  tightly  ctfrked  with  exclusion  of  air.  Place  one 
tube  in  the  dark,  the  other  in  direct  sunlight.  Note  the  change  in 
hydrogen-ion  concentration  in  the  two  tubes  after  2-3  hours  or 
less  if  the  sunlight  proves  injurious  to  the  planaria.  If  the  planaria 
give  out  CO2  the  solution  should  become  more  acid,  if  they  use 
up  CO2  the  solution  should  become  more  alkaline. 

(2)  Repeat  the  experiment  using  a  water  plant,  e.g.,  spirogyra, 
instead  of  the  planaria,  and  having  the  water  distinctly  acid  to 
start  with  by  bubbling  through  it  CO2  from  your  breath. 

In  the  tube  placed  in  sunlight  bubbles  may  appear  and  a  gas 
collect.  Determine  the  nature  of  this  gas  by  an  appropriate  test. 


**-/          A^^^y  M+^**<4_jfa.  x«-£< 
•/T?-'  V™  CHAPTER.  } 


C    f^4^r/^^. 

^  Capillary  Circulation. 

Pith  a  frog  without  haemorrhage.     Pin  web  of  foot  over  a  hole  in 
a  board.    Keep  rr^j06t  with  saline.    Cover  with  coverglass  if  neces- 
i     sary.     Focus  on  web  with  CPp.  microscope. 

1.  Blood  Vessels.     Notice  the  movement  of  the  blood  within 
the    blood  vessels  of  varying  size  and  irregular  course. 

2.  Velocity  of  flow.     Is  the  motion  equally  rapid  in  all  the 
vessels?     If  not  are  the  slower  currents  in  the  larger  or  smaller 
channels?    How  can  you  distinguish  an  artery  from  a  vein?    Com- 
pare thickness  of  walls  and  character  of  flow.     Is  the  velocity 
equally  rapid  in  all  parts  of  a  vessel  at  a  given  point?    Why  is  this 

'so?    Of  what  physiological  importance? 

3.  Pulse.    Have  you  seen  evidence  of  intermittent  force  acting 
upon   the   corpuscles?     If  so   describe   its   influence.      Determine 
whether  this  intermittent  force  makes  itself  evident  in  all  of  the 
vessels.     If  not,  in  which  class  of  vessels  is  it  present?     Can  you 
detect  pulsations  in  a  small  artery?    Vein?     Capillary? 

4.  Size  of  Vessels.     Do  you  observe  any  variation  in  the  size 
of  a  given  vessel?     Carefully  measure  with  the  eyepiece  micro- 
meter and  determine. 

5.  Do  you  see  small  vessels  appear,  apparently  new,  from  time 
to  time?    How  do  you  account  for  this?    Do  you  see  small  vessels 
apparently  disappear? 

6.  Corpuscles.     In  the  frog  the  red  corpuscles  are  larger  than 
the  white.     With  high  power  study  the  behaviour  of  the  red  cor- 
puscles.    Do  they  change  shape?     If  so,  under  what  conditions? 
Do  you  see  evidences  of  flexibility  and  elasticity?     Are  the  red 
corpuscles  nucleated?     Study  the  white  corpuscles.     Where  are 
they  the  most  numerous  in  the  blood  stream?    How  do  you  account 
for  this  distribution? 

7.  Capillary  Flow.     Estimate  the  velocity,  of  a  single  corpuscle 
by  means  of  the  micrometer  eyepiece  and  stop  watch.     Of  what 
physiological  significance  is  this  slow  rate? 

273 


274  EXPERIMENTAL  PHYSIOLOGY 

8.  Process  of  Inflammation.  Remove  the  cover-glass,  dry  the 
web  with  filter  paper  and  touch  a  point  with  a  pin  dipped  into  a 
2  per  cent,  solution  of  croton  oil  and  olive  oil.  Without  replacing 
cover  glass,  with  low  power,  observe  whether  the  presence  of  the 
croton  oil  effects  any  change  in  the  diameter  of  the  vessels,  or  in 
the  rate  of  blood-flow.  If  there  is  a  change  in  both,  has  one  a  causa- 
tive relation  to  the  other?  Note  and  describe  minutely  all  changes 
which  take  place  at  or  near  the  place  touched  with  the  croton  oil. 
If  no  marked  changes  have  been  produced  in  10  minutes  by  the 
croton  oil,  touch  the  point  with  a  needle  which  has  been  dipped 
in  strong  nitric  acid.  Observe  with  high  power,  using  cover-glass. 
Describe  process  of  extravasation  of  white  or  red  corpuscles. 

^Lymph-Heart^. 


Another  method  of  pertorn 
results.    The  tongue  of  a  pith 


are  readily  seen.    A  drop  of  x> 


produce  the  necessary  inflamn  ation. 


ng  this  experiment  also  gives  good 
d  frog  is  pinned  out  over  a  hole  in 


a  board.     With  the  proper  d(  gree  of  stretching  the  bloodvessels 


ol  on  the  surface  of  the  tongue  will 


1.  Posterior  Lymph-Hearts.  Stretch  the  pithed  frog  out, 
ventral  side  down,  and  watch  the  beating  of  the  posterior  pair  of 
lymph-hearts.  These  hearts  are  located  (at  the  dorsal  posterior 
end  of  the  body)  one  on  each  side  of  the  urostyle  in  the  triangular 
spaces  easily  observed  there  between  certain  muscle  attachments. 

Cautiously  turn  back  the  skin  covering  the  lymph-hearts  being 
careful  not  to  injure  the  cutaneous  veins  and  thus  cause  bleeding. 
Moisten  exposed  parts  with  normal  salt  solution  when  necessary, 
and  count  the  number  of  beats  per  minute  of  each  lymph-heart. 
Compare.  The  movements  of  the  blood-heart  can  be  distinguished 
without  opening  the  chest.  Can  you  detect  any  synchronous 
relation  between  the  rhythm  of  the  blood-heart  and  that  of  the 
lymph-hearts? 

Blood-heart. 

1.  Blood  heart-of  the  Frog.  Expose  the  blood-heart.  Observe 
the  heart  "in  situ"  noting  the  two  auricles;  the  ventricle;  the 
auriculo-ventricular  groove;  and  the  truncus  arteriosus,  which  pro- 
jects anteriorly  from  the  ventricle  in  front  of  the  auricles  and 
divides  into  the  two  aortae. 


PHYSIOLOGY  OF  CIRCULATION  275 

Tilt  up  the  ventricle  and  observe  the  thin  shred  of  connective 
tissue — the  frenum  (containing  a  small  vein) — -passing  from  the 
pericardium  to  the  back  part  of  the  ventricle.  Tie  a  fine  thread 
around  the  frenum  and  divide  it  dorsal  to  the  ligature.  Lift  the 
heart  gently  by  this  thread  and  observe  also  the  sinus  venosus, 
continuous  with  the  right  auricle  and  formed  by  the  union  of  the 
inferior  and  the  two  (smaller)  superior  venae  cavae. 

2.  Arrange  to  record  heart  beat  on  slow  kymograph.     Rate  of 
heart  beat  and  influence  of  temperature. 

(a)  Determine   and   record   the   normal   rate   per   minute   by 
counting  several  times. 

(b)  Determine  and  record  the  rate  per  minute  after  bathing 
the  heart  by  means  of  a  pipette  with  a  few  c.c.  of  normal  saline  at 
20°  C.;at30°  C.  and  5°  C. 

3.  Movements  and  Sequence  of  Contraction. 

(a)  Keep  the  heart  beat  slowed  down  with  the  cold  normal 
saline  and  it  will  be  possible  to  determine  the  sequence  and  details 
of  contraction.     Determine  whether  the  two  auricles  contract  at 
the  same  time.  * 

Carefully  lift  the  ventricle  by  the  ligature  of  the  frenum  and 
observe  the  sinus  venosus.  Note  where  the  wave  of  contraction 
really  begins  and  follow  the  whole  cycle  of  contraction  step  by 
step.  Tabulate  and  describe  the  events  in  order  through  one 
entire  cycle. 

(b)  Use  a  pithing  needle  now  to  destroy  the  entire  spinal  cord. 
What  effect  do  you  observe  upon  the  beating  of  the  lymph  hearts? 
What  can  you  conclude  concerning  the  nerve  centres  which  govern 
their  movements?    Is  any  change  produced  in  the  beat  or  appear- 
ance of  the  blood-heart?     Conclusions? 

4.  Effect   of  Temperature   on   the   Excised   Heart.      Carefully 
remove  the  entire  heart  from  the  body. 

(a)  Place  the  watch  glass  containing  the  excised  heart  on  a 
small  beaker  of  warm  water — determine  the  rate  per  second  at 
5°  C.,  at  20°  C.  and  at  35°  C.    Caution:  Do  not  let  the  temperature 
rise  above  40°  C.     Plot  beat  curve  and  calculate  Q  10. 

(b)  Section  of  the  excised  heart.     Separate  the  sinus,  auricles 
and  ventricle  from  each  other.     Does  each  beat  independently?    Do 
they  beat  at  the  same  rates?     Note  time  for  10  pulsations  of  each. 


,So^    -r 
~.    6s»j£.    fi/^/Yt^tA 


St. 


^^ 

" 


APPENDIX. 


TABLE  I. 

THE  PERCENTAGE  OF  OXYGEN  WHICH  IS  EQUIVALENT  TO  THE  NlTROGEN  FOUND 

IN  THE  EXPIRED  AIR. 

To  obtain  the  nitrogen  in  the  expired  air,  add  the  percentage  of  COz  and  C>2 
found  and  subtract  the  sum  from  100.  The  table  gives  the  percentage  for  O2 
corresponding  to  this  figure: 

%N2  78.7     78.8     78.9     79.0    79.1     79.2     79.3     79.4    79.5    79.6    79.7    79.8 

79.9    80.0    80.1     80.2    80.3     80.4    80.5    80.6 
%O2  20.86  20.88  20.90  20.93  20.96  20.98  21.01  21.04  21.07  21.10  21.12  21.14 

21.16  21.19  21.22  21.25  21.28  21.31  21.35  21.38 


TABLE  II. 

TENSION  OF  AQUEOUS  VAPOUR  IN  MILLIMETRES  OF  MERCURY. 
To  obtain  the  dry  barometric  pressure,  subtract  the  mm.  Hg.  corresponding  to 
the  temperature  of  the  air  from  the  barometric  pressure  at  the  time  of  the  experi- 
ment: 

Temp.      15°C.  16°       17°       18°       19°       20°       21°       22°       23°       24°       25° 
Mm.         12.7     13.5     14.4     15.4     16.3     17.4     18.5      19.7     20.9     22.2     23.5 


TABLE  III. 

TEMPERATURE  CORRECTIONS  TO  REDUCE  READINGS  OF  A  MERCURIAL 

BAROMETER  WITH  A  BRASS  SCALE  TO  0°  C. 

Subtract  the  appropriate  quantity  as  found  in  table  from  the  height  of  the 
barometer.  The  table  is  for  a  barometer  with  a  brass  scale,  and  the  values  are  a 
little  lower  (about  .2  mm.)  than  for  the  glass  scale.  The  corrections  for  inter- 
mediate temperatures  can  be  approximated. 


Temp. 

700 

710 

720 

730 

740 

750 

760 

770 

mm. 

mm. 

mm. 

mm. 

mm. 

mm. 

mm. 

mm. 

15°C. 

1.69 

1.72 

1.74 

1.77 

1.79 

1.81 

1.84 

1.86 

20° 

2.26 

2.22 

2.32 

2.36 

2.39 

2.42 

2.45 

2.48 

25° 

•2.83 

2.87 

2.91 

2.95 

2.99 

3.03 

3.07 

3.11 

277 

278  EXPERIMENTAL  PHYSIOLOGY 


TABLE  IV. 

TABLE  FOR  REDUCING  GASEOUS  VOLUMES  TO  NORMAL  TEMPERATURE  AND 

PRESSURE. 

The  observed  volume,  when  multiplied  by  the  factor  corresponding  to  the 
temperature  and  pressure,  will  give  the  volume  of  the  expired  air  reduced  to  0°c. 
and  760  mm. 


Mm. 

15°C. 

16° 

17° 

18° 

19° 

20° 

21° 

22° 

23° 

24° 

25° 

720 

.898 

.894 

.891 

.888 

.885 

.882 

.880 

.877 

.873 

.870 

.857 

730 

.910 

.907 

.904 

.901 

.897 

.894 

.891 

.888 

.885 

.882 

.879 

740 

.922 

.919 

.916 

.913 

.910 

.907 

.904 

.901 

.897 

.894 

.891 

750 

.935 

.932 

.928 

.925 

.922 

.919 

.916 

.913 

.910 

.907 

.904 

760 

.947 

.944 

.941 

.938 

.934 

.931 

.928 

.925 

.922 

.919 

.916 

770        .960      .957      .953      .950      .948      .945      .940     .938      .933      .930      .927 


APPENDIX 


279 


TABLE  V. 


R.  Q.      CALORIES  FOR  1  LITER 

Number 


RELATIVE  CALORIES  CONSUMED  AS 

Carbohydrate  Fat 


per  cent. 

per  cent. 

0.707 

4.686 

0 

100 

0.71 

4.690 

1.4 

98.6 

0.72 

4.702 

4.8 

95.2 

0.73 

4.714 

8.2 

91.8 

0.74 

4.727 

11.8 

88.4 

0.75 

4.739 

15.0 

85.0 

0.76 

4.752 

18.4 

81.6 

0.77 

4.764 

21.8 

78.2 

0.78 

4.776 

25.2 

74.8 

0.79 

4.789 

28.6 

71.4 

0.80 

4.801 

32.0 

68.0 

0.81 

4.813 

35.4 

64.6 

0.82 

4.825 

38.8 

61.2 

0.83 

4.838 

42.2 

57.8 

0.84 

4.850 

45.6 

54.4 

0.85 

4.863 

49.0 

51.0 

0.86 

4.875 

52.4 

47.6 

0.87 

4.887 

55.8 

44.2 

0.88 

4.900 

59.2 

40.8 

0.89 

4.912 

62.6 

37.4 

0.90 

4.924 

66.0 

34.0 

0.91 

4.936 

69.4 

30.6 

0.92 

4.948 

72.8 

27.2 

0.93 

4.960 

76.2 

23.8 

0.94 

4.973 

79.6 

20.4 

0.95 

4.685 

83.0 

17.0 

0.96 

4.997 

86.4 

13.6 

0.97 

5.010 

89.8 

10.2 

0.98 

5.022 

93.2 

6.8 

0.99 

5.034 

96.6 

3.4 

1.00 

5.047 

100.0 

0.0 

(From  Lusk.) 

INDEX 


Aberration,  chromatic,  150 

spherical,  149 

Accelerator  fibres  of  heart,  63 
Acceleration  of  heart,  63 
Accommodation,  153 

reflex,  155 
Acoustic  reflex,  249 

Action,  of  CO2,  ether  and  chloroform 
on  nerve,  58,  50 

of  cations  on  cardiac  muscle,  70,  62 

current,  41 

pumping,  of  heart,  223 
Adrenalin,  effect  of,  on  blood  vessels  in 
frog,  77 

influence  of,  on  mammalian  heart, 

209 

Adsorption,  266 
Aesthesiometer,  194 
After  images,  174 

All-or-None  principle  in  cardiac  mus- 
cle, 61 

in  nerve  and  voluntary  muscle,  57 
Alveolar  air,  collection  of,  112 
Analysis  of  gases,  107 

of  tetanus,  37 

Anelectrotonus  in  nerve,  51 
Anodal  contractions  in  heart,  55 
Aqueous  vapor,  tension  of,  277 
Asphyxia,  influence  of,  on  blood  pres- 
sure, 201 

effect  of,  on  kidney  volume,  205 
Astigmatism,  151 

Atropine,  influence  of  on  submaxillary 
secretion,  227 

on  heart,  65 
A-V  interval,  turtle,  67 


Basis  of  sound,  182 

Bellows  recorder,  use  of,  202 

Bile,  secretion  of,  228 

Binocular  vision,  181 

Blind  spot,  166 

Blood  flow,  measurement  of,  by  calori- 

metric  method,  210 
Blood  gas,  determination, 

chemical  method,  128 

pump  method,  122 

Blood  pressure,  method  of  determining 
in  lower  animals,  79 

measurement  of,  in  man,  71 
Blood  pump,  122 


Blood  vessels,  response  of,  to  chemical 

substances,  76 
Bones  of  middle  ear,  186 
Brodie's  apparatus  for  heart  per- 

fusion,  207 
Buffer  action,  268 

Calcium   ions,   action   of,   on    cardiac 
muscle,  70 

influence  of,  on  mammalian  heart, 
209 

influence  of,  on  turtle  heart,  70 
Calculation  of  respiratory  quotient,  118 
Calorimetric  method  for  measurement 

of  blood  flow,  210 
Capillary  circulation,  273 
Carbon  dioxide,  action  of  on  nerve,  50 

combining  power  of  the  alkaline 
reserve  of  blood,  138 

influence  of,  in  lowering  the  disso- 
ciation curve,  137 
Cardiac  muscle,  61 
Cardiograms,  96 
Carotid  pulse,  94 

Cations,  action  of,  on  cardiac  muscle, 
62 

influence  of,  on  mammalian  heart, 
209 

influences  of,  on  turtle  heart,  70 
Central  nervous  system,  239 
Cells,  physical  chemistry,  263 
Cerebral  localization,  243 
Cerebrum,  function  of 

in  frog,  102 

in  mammal,  243 

in  pigeon,  253 
Chemical  substances,  response  of  blood 

vessels  to,  71 

Chloroform,  action  on  nerve,  50 
Chromatic  aberration,  150 
Ciliated  cells,  45 
Circulation,  reflex  control  of,  199 

capillary,  273 

scheme,  74 

time,  90 
Coagulation  of  muscle  proteins,  39 

of  blood,  91 
Cochlea,  188 
Cold  spots,  192 
Colloids,  263 
Colour  biindfless,  175 

vision,  170 


281 


282 


EXPERIMENTAL  PHYSIOLOGY. 


Colours,  complementary,  172 
Compensatory  pause  in  heart,  69 
Conduction  of  a  nerve  fibre  in  both 

directions,  46 
Contraction,  isometric,  27 

istonic,  25 

simple,  22 

Contrast,  simultaneous,  173 
Control  of  pancreatic  secretion.  228 
Corrections  for  a    barometer    with    a 

brass  scale,  277 
Corti,  organ  of,  189 
Curare,  effect  of,  19 

influence  on  respiration,  200 
Current  of  injury,  40 

Dark  adaption  of  retina,  167 

Decerebrate,  activities  of  frog,  102 
activities  of  pigeon,  253 
rigidity,  249 

Decerebrator,  247 

Deglutition  reflex,  249 

Depressor  nerve  stimulation  effect  on 
blood  pressure,  89 

Digestion,  267 

Digestive  system,  226 

Diphasic  variation,  in  muscle,  40 
in  nerve,  56 

Direct  current  stimulation,  54 

Dissociation  curve  for  Oxygen  and 
CO2,  combining  power  of  blood, 
132 

Duodenal  extract,  influence  of,  on  pan- 
creatic secretion,  229 

Effect  of  drying  on  muscle,  16 

of  temperature  on  contraction,  28 

of    temperature    on    contraction, 
apparatus  for,  29 

of  temperature  on  cardiac  muscle, 

62 

Efferent  nerve  fibres,  46 
Elasticity  of  muscle,  20,  42 
Electrical  changes  in  muscle,  39 

changes,  influence  of,  on  nerve,  51 

stimulation,  9,  15 
Electrodes,  Sherrington,  237 
Electrotonus  in  the  heart,  55 

in  nerve,  51 
Enzymes,  267 

Epinephrin,    influence    of,    on    mam- 
malian heart,  209 

resuscitation  by  transfusion  with, 

205 

Errors  in  refraction,  149 
Ether,  action  on  nerve,  50 
Eustachian  tube,  function  of,  188 


Extensor  thrust,  240 
Extra  systole,  68 

Factors    influencing    nervous    conduc- 
tion, mechanical,  50 

Thermal,  50 

Chemical,  50 
Fatigue,  33 

resistance  of  nerve  to,  57 

reflex,  241 
Fistula,  gastric,  234 

of  parotid  gland,  231 
Fixation  of  tracing,  12 
Flexion  reflex,  240,  249,  256 
Fovea  centralis,  163 
Frog's  heart,  study  of,  61 

Gad's  method  for  cardiac  valves,  224 

Gas  analysis  apparatus,  107 

Gaseous    volume    reduced    to    normal 

temperature  and  pressure,  278 
General  Physiology,  258 
Gastric  fistula,  234 
Glucose,  influence  of,  on   lymph  flow, 

220 

Graded  stimulation,  effect  of,  17 
Graphic  record,  12 
Gunn's  apparatus  for  heart  perfusion, 

207 

Haemodynamics,  principles  of,  73,  78 
Haemorrhage,  effect  of,  on  blood  pres- 
sure, 84 
Haldane's  apparatus  for  blood  gases, 

129 

Head-shake  reflex,  249 
Hearing,  182 
Heart    beat     observed    in    the    open 

thorax,  85 
contraction,     suspension     method 

for,  63 

perfusion,  mammalian,    206 
Hering's  theory  of  color  vision,  176 
Heat  production,  38 
rigor,  39 
spots,  193 
Hunger  contractions,  observations  of, 

235 
Hydrogen  ions,  266 

influence  of,  on  mammalian  heart, 

209 

Hypermetropia,  151 
Hyperpnea,  200 

Images,  Purkinje,  156 

Inadequate  stimuli,  summation  of,  48 

Independent  excitability  of  muscle,  19 


INDEX 


283 


Induction,  immediate  successive,  242 
Inductorium,  11 
Inflammation,  174 
Inhibition,  reciprocal,  251 

of  the  heart,  62 

of  reflexes,  101 
Innervation,  reciprocal,  245 

of  salivary  glands,  226 
Intestines,  movements  of,  236 
Irritability  of  smooth  muscle,  42 
Isometric  contraction,  27 
Isotonic  contraction,  25 

Judgment  of  space  and  depth,  178 
Jugular  pulse  curve,  95 

Katelectrotonus  in  nerve,  51 
Kathodal  contractions  in  the  heart,  55 
Kidney    volume,    change    in    due    to 
asphyxia,  205 

change  in  due  to  splanchnic  stimu- 
lation, 203 

Knee  jerk,  105,  240,  249,  256 
Kymograph,  rapid,  23 

slow  moving,  16 

Harvard.  26 


Latent  period  of  muscle  contraction 

voluntary  muscle,  24 

smooth  muscle,  43 
Lens,  attachment  of,  154 
"Light  reflex",  167 
Load  and  work,  31 
Localization  cerebral,  243 
Long-sightedness,  151 
Lymph  flow,  influences  of 

circulatory  changes  on,  218 

lymphagogues  on,  220 

Macula  lutea,  163 

Maximal  and  minimal  stimulation,  17 

Measurement    of    blood    flow    calori 

metric  method,  210 
Mechanical  stimulation,  16 
Membrane,  semi-permeable,  263 
Metabolism  in  nerve,  56 
Middle  ear,  186 
Monocular  vision,  180 
Movements  of  intestine,  236 
Muscle    contractions,    apparatus    for 

recording,  16 
sense,  197 

Muscles  of  the  frog's  leg,  21 
Musical  sound  waves,  184 
Myopia,  151 


Near  point,  155 

Nerve,  conduction  of,  in  both  direc- 
tions, 46 
Nerve-muscle  preparation,  14 

as  a  rheoscope,  40 
Nervous  control  of  heart  beat,  62 

impulse  velocity  of,  48 
Nicotine,  effect  of,  on  heart,  65 
Nodal  point,  144 

Oesophagus,  movements  of,  236 
Oncometer,  use  of,  202 
Ophthalmoscope,  use  of,  158 

by  direct  method,  160 

by  indirect  method,  161 
Optics,  physiological,  139 
Osmasis,  264 
Overtones,  185 
Oxidation  in  the  body,  90 
Oxygen,  percentage  of,  equivalent  to 

nitrogen  in  expired  air,  277 

Pain,  sense  of,  196 

Pale  muscle  fibres,  38 

Palpebral  reflex,  104 

Pancreatic  secretion,  control  of,  228 

Parotid  gland,  fistula  of,  231 

Peptone,  influence  of,   on  lymph  flow, 

221 
Perfusion  of  the  frog,  76 

of  excised  mammalian  heart,  206 

turtle  heart,  69 
Physical  basis  of  sound,  182 
Pigeon,  decerebrate,  253 
Pinna  reflex,  248 
Pitch,  182 
Pithing,  15 

Pituitrin,  influence  on  lymph  flow,  221 
Plants,  responses  of,  271 
Plasmolysis,  259 
Polyshygmograph,  93 
Posterior  columns  of  spinal  cord,  stim- 
ulation of,  256 
Postural  tonus,  reflex,  250 
Potassium  ions,  action  of,  on  cardiac 
muscle,  62 

influence  of,  on  mammalian  heart, 

209 

Preliminary  technique,  9 
Preparation  of  cat  and  dog  for  experi- 
mental study,  79 

of  rabbit,  87 
Primary  circuit,  10 
Principal  axis,  143 
Propagation  of  pulse  wave,  93 
Protoplasm  properties,  258 

chemistry,  261 


284 


EXPERIMENTAL  PHYSIOLOGY. 


Purkinje  figures,  165 
images,  156 


Radial  pulse,  94 
Rapid  kymograph,  23 
Reaction  time  in  man,  106 
Reciprocal  inhibition,  251 

innervation,  245 
Red  muscle  fibres,  38 
Reflection,  laws  of,  139 
Reflex,  accommodation,  155 

acoustic,  249 

action  in  frog,  98 

action  in  mammal,  239 

control  of  circulation,  199 

deglutition,  249 

extensor  thrust,  240 

fatigue,  241 

flexion,  240,  249,  256 

head  shake,  249 

palpebral,  104 

pinna,  248 

postural  tonus,  250 

control  of  respiration,  199 

scratch,  240 

summation,  241 

time  240 

time  in  frog,  99 

time,  in  man,  106 
Reflexes,  spreading  of,  99 

inhibition  of,  101 
Refraction  by  a  convex  lens,  145 

errors  in,  149 

in  the  eye,  146 
Refractive  index,  143 
Refractory  period  in  the  heart,  68 
Removal  of  paper  from  drum,  12 
Resistance  of  nerve  to  fatigue,  57 
Respiration,  107 

reflex  control  of,  199 
Respiratory  exchange  in  man,  118 

movements,  influence  of,  on  pulse 
97 

quotients,  279 

quotients,  calculation  of,  120 
Response  of  retina  to  light,  167 
Resuscitation     by     transfusion     with 

epinephrin,  205 

Retina,  effects  on,  of  stimulating  with 
two  different  colours,  171 

structure  of,  163 

response  to  light,  157 
Retinoscope,  161 
Rheoscope,  nerve  muscle  as  a,  40 
Rhythmicity  of  smooth  muscle,  43 
Rigor  mortis,  39 


Salivary  glands,  innervation  of,  226 
Saliva,  secretion  of,  231 
Scheiner's  experiment,  157 
Schematic  eye,  147 

Sciatic  stimulation,  effect    on    respira- 
tion, 199 

Scratch  reflex,  240,  256 
Secondary  circuit,  10 
Secretin,  influence  of,  on  pancreatic 

secretion,  230 
Secretion  of  bile,  228 
of  gastric  juice,  233 
of  pancreas,  228 
of  saliva,  231 

of  submaxillary  gland,  226 
Semilunar   valve,    effect  of  damaging, 

223 

Semipermeable  membranes,  263 
Sensations,  skin,  192 
Sherrington  electrodes,  237 
Simple  contractions,  22 
Simultaneous  action  on  the  retina  of 

three  primary  colours,  173 
Skin  sensations,  192 
Smoking  paper,  12 
Smooth  muscle,  42 
Sodium  chloride,  influence  of  on  lymph 

flow,  221 
Sodium    ions,    action    of,    on    cardiac 

muscle,  62 

Sound  waves,  diagrams,  183,  184 
Sodium  nitrite,  effect  of,   on  blood  ves- 
sels of  the  frog,  77 
Sound  waves,  transmission  of,  in  the 

ear,  185 

Space  and  depth,  judgments  of,  178 
Special  senses,  139 
Spherical  aberration,  149 
Sphygmic  period,  96 
Spinal  cat,  255 
Spinal  nerve  roots,  function  of,  frog,  102 

functions  of  mammal,  245,  250 
Spirometer,  Tissot-Carpenter,  118 
Splanchnic  nerve  stimulation  effect  on 

blood  pressure,  83 
stimulation,  effect    of,    on  kidney 

"volume,"  202 
Spreading  of  reflexes,  99 
"Staircase"  effects,  33 
Stannius  ligature,  65 
Stereoscopic  vision,  181 
Stewart's  calorimeter  method  for  meas- 
urement of  blood  flow,  210 
Submaxillary  gland,  secretion  of,  226 
Summation  of  inadequate  stimuli,  48 
of  smooth  muscle,  43 
from  two  stimuli,  35 


INDEX 


285 


Surface  tension,  264 
Suspension    method    for    heart    con- 
traction, 63 


Table 

percentage  of  oxygen  equivalent  to 

nitrogen  in  expired  air,  277 
temperature  corrections  to  reduce 
readings  of  a   mercurial 
barometer  with   a   brass 
scale,  277 

tension  of  aqueous  vapour,  277 
for  reducing  gaseous  volumes  to 
normal  temperature  and  pres- 
sure, 278 

of  respiratory  quotients,  279 
Taste,  197 
Temperature,  effect  of,  on  contraction, 

28 
Temperature  sense,  193 

effects  on  cardiac  muscle  of  frog,  62 
effects  on  cardiac  muscle  of  turtle, 

68 

Tension  of  aqueous  vapour,  277 
Tetanic  nature  of  voluntary  contrac- 
tion, 36 
Tetanus,  35 

of  smooth  muscle,  44 
Thermal  stimulation,  15 
Thoracic  duct,  dissection  for  exposure 

of,  218 

Tissot-Carpenter     method     for    deter- 
mining respiratory  exchange,  118 
Tone  of  smooth  muscle,  43 
Touch,  sense  of,  194 
Transfusion,  effect,  on  blood  pressure,  84 


Transmission  of  sound  waves  in  the  ear, 

185 

Tropisms,  269 

Tricuspid  valve,  operation  of,  223 
Turtle  heart,  study  of,  66 

Vagus,  influence  on  heart,  62 

influence  on  respiration,  199 
nerve  in  the  frog,  location  of,  64 
stimulation,  effect  on  blood  pres- 
sure (dog),  81 

stimulation,  effect  on  blood  pres- 
sure (rabbit),  89 
Van't  Hoff  rule,  259 
Valves  of  the  heart,  action  of,  206 
Vasoconstrictor  nerves,  demonstration 
of  in  cervical  sympathetic,  87 
fibres,  demonstrated  by  the  ple- 

thysmograph,  202 
Velocity  of  the  nervous  impulse,  48 

of  transmission  of  pulse  wave,  93 
Venous  curve,  interpretation  of,  95 
Veratrine,  influence  of,  on  contraction, 

32 

Vision,  123 
Visual  axis,  151 

Volume  of  a  contracting  muscle,  25 
Voltage,  9 
Voluntary  muscle,  14 

contraction,  tetanic  nature  of,  35 

Wave  of  contraction,  24 
Work,  load  and,  31 
Writing  point,  12 

Young-Helmholtz    theory    of    colour 
vision,  176 


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